Add wx/gtk/private/wrapgtk.h wrapping gtk/gtk.h in pragmas disabling
these warnings and include it everywhere instead of directly including
gtk/gtk.h.
Also include wx/gtk/private/gtk2-compat.h from this wrapper header as it
was included by 90% of the files including gtk/gtk.h itself and it seems
to be better and simpler to just always include it.
The headers for this compiler, at least in the version packaged under Debian,
define BCN_DROPDOWN but not the NMBCDROPDOWN struct we also need, so we have
no choice but to redeclare the struct ourselves to allow this code to compile.
Leave ownership of the native window to the user code as it may want to reuse
it for some other purpose and provide an explicit Disown() function that can
be called if the user really wants wxWidgets to take ownership of the native
window.
In particular, this avoids problems when using ARC under OS X which resulted
in a double "release" before.
Define BS_SPLITBUTTON ourselves if it's not defined in the headers to at
least create the control even then. Skip the code handling BCN_DROPDOWN as
it's too much trouble to make it compile with the old headers however.
This should fix the build with VC8 currently failing on buildbot.
