added _eglGet*Handle() functions

These are the inverse of the _eglLookup*() functions.
Returns the public handle for a private surface/config/display/etc.
Removes glapi.c's direct access of private fields.

src/egl/main/egldisplay.h

@@ -24,6 +24,10 @@ extern _EGLDisplay *
 _eglNewDisplay(NativeDisplayType displayName);
 
 
+EGLDisplay
+_eglGetDisplayHandle(_EGLDisplay *display);
+
+
 extern _EGLDisplay *
 _eglLookupDisplay(EGLDisplay dpy);