Rework symbol visibility for easier maintenance

Save in a few special cases, _X_EXPORT should not be used in C source
files. Instead, it should be used in headers, and the proper C source
include that header. Some special cases are symbols that need to be
shared between modules, but not expected to be used by external drivers,
and symbols that are accessible via LoaderSymbol/dlopen.

  This patch also adds conditionally some new sdk header files, depending
on extensions enabled. These files were added to match pattern for
other extensions/modules, that is, have the headers "deciding" symbol
visibility in the sdk. These headers are:
o Xext/panoramiXsrv.h, Xext/panoramiX.h
o fbpict.h (unconditionally)
o vidmodeproc.h
o mioverlay.h (unconditionally, used only by xaa)
o xfixes.h (unconditionally, symbols required by dri2)

  LoaderSymbol and similar functions now don't have different prototypes,
in loaderProcs.h and xf86Module.h, so that both headers can be included,
without the need of defining IN_LOADER.

  xf86NewInputDevice() device prototype readded to xf86Xinput.h, but
not exported (and with a comment about it).

hw/xfree86/i2c/xf86i2c.c

@@ -358,7 +358,7 @@ I2CAddress(I2CDevPtr d, I2CSlaveAddr addr)
  * Don't expect a read- or write-only device will respond otherwise.
  */
 
-_X_EXPORT Bool
+Bool
 xf86I2CProbeAddress(I2CBusPtr b, I2CSlaveAddr addr)
 {
     int r;
@@ -439,7 +439,7 @@ I2CWriteRead(I2CDevPtr d,
 
 /* wrapper - for compatibility and convinience */
 
-_X_EXPORT Bool
+Bool
 xf86I2CWriteRead(I2CDevPtr d,
 		 I2CByte *WriteBuffer, int nWrite,
 		 I2CByte *ReadBuffer,  int nRead) 
@@ -451,7 +451,7 @@ xf86I2CWriteRead(I2CDevPtr d,
 /* Read a byte, the only readable register of a device.
  */
 
-_X_EXPORT Bool
+Bool
 xf86I2CReadStatus(I2CDevPtr d, I2CByte *pbyte)
 {
     return xf86I2CWriteRead(d, NULL, 0, pbyte, 1);
@@ -460,7 +460,7 @@ xf86I2CReadStatus(I2CDevPtr d, I2CByte *pbyte)
 /* Read a byte from one of the registers determined by its sub-address.
  */
 
-_X_EXPORT Bool
+Bool
 xf86I2CReadByte(I2CDevPtr d, I2CByte subaddr, I2CByte *pbyte)
 {
     return xf86I2CWriteRead(d, &subaddr, 1, pbyte, 1);
@@ -470,7 +470,7 @@ xf86I2CReadByte(I2CDevPtr d, I2CByte subaddr, I2CByte *pbyte)
  * sub-address of the first register.
  */
 
-_X_EXPORT Bool
+Bool
 xf86I2CReadBytes(I2CDevPtr d, I2CByte subaddr, I2CByte *pbyte, int n)
 {
     return xf86I2CWriteRead(d, &subaddr, 1, pbyte, n);
@@ -480,7 +480,7 @@ xf86I2CReadBytes(I2CDevPtr d, I2CByte subaddr, I2CByte *pbyte, int n)
  * determined by its sub-address.
  */
 
-_X_EXPORT Bool
+Bool
 xf86I2CReadWord(I2CDevPtr d, I2CByte subaddr, unsigned short *pword)
 {
     I2CByte rb[2];
@@ -495,7 +495,7 @@ xf86I2CReadWord(I2CDevPtr d, I2CByte subaddr, unsigned short *pword)
 /* Write a byte to one of the registers determined by its sub-address.
  */
 
-_X_EXPORT Bool
+Bool
 xf86I2CWriteByte(I2CDevPtr d, I2CByte subaddr, I2CByte byte)
 {
     I2CByte wb[2];
@@ -510,7 +510,7 @@ xf86I2CWriteByte(I2CDevPtr d, I2CByte subaddr, I2CByte byte)
  * sub-address of the first register.
  */
 
-_X_EXPORT Bool
+Bool
 xf86I2CWriteBytes(I2CDevPtr d, I2CByte subaddr, 
 		  I2CByte *WriteBuffer, int nWrite)
 {
@@ -536,7 +536,7 @@ xf86I2CWriteBytes(I2CDevPtr d, I2CByte subaddr,
  * determined by its sub-address.
  */
 
-_X_EXPORT Bool
+Bool
 xf86I2CWriteWord(I2CDevPtr d, I2CByte subaddr, unsigned short word)
 {
     I2CByte wb[3];
@@ -555,7 +555,7 @@ xf86I2CWriteWord(I2CDevPtr d, I2CByte subaddr, unsigned short word)
  * remain uninitialized.
  */
 
-_X_EXPORT Bool
+Bool
 xf86I2CWriteVec(I2CDevPtr d, I2CByte *vec, int nValues)
 {
     I2CBusPtr b = d->pI2CBus;
@@ -595,7 +595,7 @@ xf86I2CWriteVec(I2CDevPtr d, I2CByte *vec, int nValues)
  * the least significant bit, indicating a read or write access, to zero.
  */
 
-_X_EXPORT I2CDevPtr
+I2CDevPtr
 xf86CreateI2CDevRec(void) 
 {
     return xcalloc(1, sizeof(I2CDevRec));
@@ -605,7 +605,7 @@ xf86CreateI2CDevRec(void)
  * you should set <unalloc> to free it.
  */
 
-_X_EXPORT void
+void
 xf86DestroyI2CDevRec(I2CDevPtr d, Bool unalloc) 
 {
     if (d) {
@@ -640,7 +640,7 @@ xf86DestroyI2CDevRec(I2CDevPtr d, Bool unalloc)
  * the bus-wide defaults. The function returns TRUE on success.
  */
 
-_X_EXPORT Bool
+Bool
 xf86I2CDevInit(I2CDevPtr d) 
 {
     I2CBusPtr b;
@@ -666,7 +666,7 @@ xf86I2CDevInit(I2CDevPtr d)
     return TRUE;
 }
 
-_X_EXPORT I2CDevPtr
+I2CDevPtr
 xf86I2CFindDev(I2CBusPtr b, I2CSlaveAddr addr) 
 {
     I2CDevPtr d;
@@ -690,7 +690,7 @@ static I2CBusPtr I2CBusList;
  * with safe defaults.
  */
 
-_X_EXPORT I2CBusPtr
+I2CBusPtr
 xf86CreateI2CBusRec(void) 
 {
     I2CBusPtr b;
@@ -716,7 +716,7 @@ xf86CreateI2CBusRec(void)
  * first, passing down the <unalloc> option.
  */
 
-_X_EXPORT void
+void
 xf86DestroyI2CBusRec(I2CBusPtr b, Bool unalloc, Bool devs_too) 
 {
     if (b) {
@@ -763,7 +763,7 @@ xf86DestroyI2CBusRec(I2CBusPtr b, Bool unalloc, Bool devs_too)
  * At this point there won't be any traffic on the I2C bus.
  */
 
-_X_EXPORT Bool
+Bool
 xf86I2CBusInit(I2CBusPtr b) 
 {
     /* I2C buses must be identified by a unique scrnIndex 
@@ -822,7 +822,7 @@ xf86I2CBusInit(I2CBusPtr b)
     return TRUE;
 }
 
-_X_EXPORT I2CBusPtr
+I2CBusPtr
 xf86I2CFindBus(int scrnIndex, char *name) 
 {
     I2CBusPtr p;
@@ -840,7 +840,7 @@ xf86I2CFindBus(int scrnIndex, char *name)
  * Return an array of I2CBusPtr's related to a screen.  The caller is
  * responsible for freeing the array.
  */
-_X_EXPORT int
+int
 xf86I2CGetScreenBuses(int scrnIndex, I2CBusPtr **pppI2CBus)
 {
     I2CBusPtr pI2CBus;