Merge in Win32 version: Define macro GDKVAR for declaring gdk variables

Merge in Win32 version: Define macro GDKVAR for declaring gdk variables

* gdk/gdktypes.h: Merge in Win32 version: Define macro GDKVAR for
declaring gdk variables exported/imported from the DLL. New image
type enum, GDK_IMAGE_SHARED_PIXMAP, for gdk_imlib. New drag and
drop protocol enums, GDK_DRAG_PROTO_WIN32_DROPFILES and
GDK_DRAG_PROTO_OLE2.

* gdk/gdk.h: Merge in Win32 version: Two new functions,
gdk_pixmap_create_on_shared_image and gdk_image_bitmap_new. So far
declared only for the Win32 version, but could be in the X11
version as well. (Needed for a Xlib-less gdk_imlib.)
gdk_color_hash should have only one parameter. Declare
gdk_threads_mutex with GDKVAR.

* gdk/gdkcolor.c (gdk_color_hash): As a hash function should have
just one parameter.

* gdk/gdkimage.c (gdk_image_get): Initialize bpp correctly. Bytes
per pixel, not bits.

* gdk/gdkrgb.c: Mingle includes somewhat. (gdk_rgb_select_conv):
Fetch bpp (which means bits-per-pixel here) from another place on
Win32. Accept also depth==32 (which we might get on Win32) with
bpp==32.

* gtk/{gtkclist,gtkctree,gtkdnd,gtkditable,gtkfontsel,
gtkhandlebox,gtklayout,gtkmain,gtkplug,gtkpreview,gtkrc,
gtkselection,gtksocket,gtkstyle,gtkwidget,gtkwindow}.c:
Include gdx.h from "gdkx.h", not "gdk/gdkx.h", as gdkx.h will be
in the backend-dependent directory, not in the common gdk
directory.

* gtk/testgtk.c: Ditto. Also, don't use ../gdk patchs to gdk
headers.