This macro was introduced so as to be able to be built without GLib.
However, this feature was long ago removed, and in Mutter we depend on
it anyway, so let's get rid of it in favor of more consistency.
Because the threaded-swap-wait functionality requires XInitThreads(),
and because it isn't clear that it is a win for all applications,
add a API function to conditionally enable it.
Fix the cogl-crate example not to just have a hard-coded dependency
on libX11.
https://bugzilla.gnome.org/show_bug.cgi?id=779039
Mutter (and libmutter users) are the only users of this version of
cogl, and will more or less only use the cogl-1.0, cogl-2.0 and cogl
experimental API variants, and having the possibility of having
different API versions of the same API depending on what file includes
it is error prone and confusing. Lets just remove the possibility of
having different versions of the same API.
https://bugzilla.gnome.org/show_bug.cgi?id=768977
If you include a file that might define __INSIDE_COGL_H__, don't
undefine it if it wasn't defined in that file. This makes it possible
to include for example cogl-gles2.h from some other file which defines
__INSIDE_COGL_H__.
https://bugzilla.gnome.org/show_bug.cgi?id=768976
