[Win32] Great enhancement of native look & feel for gtk+ win32. (with patch files)

["洪任諭PCMan" <pcman tw gmail com>]

Hello everyone,
I've done some imrpovement on the look & feel of gtk+ win32.
GIMP now looks more similiar to other native Win32 apps.

Here are some exciting screenshots:
http://pcman.sayya.org/gtk_win32/

The patch files are sent in separated bug reports for easier reviewing.

Here are the bug reports:
http://bugzilla.gnome.org/show_bug.cgi?id=340201
http://bugzilla.gnome.org/show_bug.cgi?id=340203
http://bugzilla.gnome.org/show_bug.cgi?id=340204
http://bugzilla.gnome.org/show_bug.cgi?id=340206

The patch for shadows of menus & tooltips are not contained in
these reports, since it's duplicated with #148535, which is still
contraversial.
See http://bugzilla.gnome.org/show_bug.cgi?id=148535