XQuartz: Integrated xpbproxy into the server.

Added a configure option called --enable-standalone-xpbproxy which is useful for deveoping xpbproxy.
The 'active' switch in preferences just disables the in-server xpbproxy (not this standalone).
(cherry picked from commit 42944936326ef8732f622db9f75b79a92980550d)

hw/xquartz/X11Application.m

@@ -50,6 +50,9 @@
 
 #include <Xplugin.h>
 
+// pbproxy/pbproxy.h
+extern BOOL xpbproxy_init (void);
+
 #define DEFAULTS_FILE "/usr/X11/lib/X11/xserver/Xquartz.plist"
 
 #ifndef XSERVER_VERSION
@@ -884,6 +887,9 @@ void X11ApplicationMain (int argc, char **argv, char **envp) {
      * an mieqEnqueue() - <rdar://problem/6300249>
      */
     check_xinitrc();
+    
+    if(!xpbproxy_init())
+        fprintf(stderr, "Error initializing xpbproxy\n");
            
     [NSApp run];
     /* not reached */