[GtkGLExt] Bug at creation of GdkGLConfig on Win32

[Michalis Kamburelis <michalis camelot homedns org>]

Hi!

While porting my program to Win32 I found a small bug in Win32 version 
of gtkglext, in file gdk/win32/gdkglconfig-win32.c, in function 
gdk_gl_config_parse_attrib_list: if attrib_list does not specify any of 
flags GDK_GL_RED_SIZE, GDK_GL_GREEN_SIZE, GDK_GL_BLUE_SIZE or 
GDK_GL_BUFFER_SIZE then pfd->cColorBits is left at default value 32. But 
this default value is too big, some graphic cards may be unable to 
supply such color precision (especially when double buffer is also 
requested).

E.g. my program is unable to obtain GdkGLConfig using gdk_gl_config_new 
with simple attrib_list
  GDK_GL_RGBA,
  GDK_GL_DOUBLEBUFFER,
  GDK_GL_ATTRIB_LIST_NONE
but when I add
  GDK_GL_BUFFER_SIZE, 0,
then I get usable GdkGLConfig.

I believe that to fix it you should simply replace line 120 of file 
gdk/win32/gdkglconfig-win32.c from
  pfd->cColorBits = 32;		/* Max */
to
  pfd->cColorBits = 0;		/* Use default color bits */

This way if I don't specify any of flags GDK_GL_RED_SIZE, 
GDK_GL_GREEN_SIZE, GDK_GL_BLUE_SIZE or GDK_GL_BUFFER_SIZE it will be 
understood that I don't care about how many bits I get in color buffer.

Regards,
Michalis.