mi: Create miPolylines as a general-purpose line drawing function

Instead of requiring all drivers to figure out which mi function to
call for each of the four cases, create a single wrapper in mi that
handles them correctly. Now drivers can simply use miPolylines in all
cases.

Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Eric Anholt <eric@anholt.net>

mi/mi.h

@@ -452,6 +452,12 @@ extern _X_EXPORT void miWideDash(DrawablePtr /*pDrawable */ ,
                                  DDXPointPtr    /*pPts */
     );
 
+extern _X_EXPORT void miPolylines(DrawablePtr pDrawable,
+                                  GCPtr pGC,
+                                  int mode,
+                                  int npt,
+                                  DDXPointPtr pPts);
+
 /* miwindow.c */
 
 extern _X_EXPORT void miClearToBackground(WindowPtr /*pWin */ ,