So that we can dynamically select what winsys backend to use at runtime
we need to have some indirection to how code accesses the winsys instead
of simply calling _cogl_winsys* functions that would collide if we
wanted to compile more than one backend into Cogl.
This moves the GLX specific code from cogl-texture-pixmap-x11.c into
cogl-winsys-glx.c. If we want the winsys components to by dynamically
loadable then we can't have GLX code scattered outside of
cogl-winsys-glx.c. This also sets us up for supporting the
EGL_texture_from_pixmap extension which is almost identical to the
GLX_texture_from_pixmap extension.
As was recently done for the GLX window system code, this commit moves
the EGL window system code down from the Clutter backend code into a
Cogl winsys.
Note: currently the cogl/configure.ac is hard coded to only build the GLX
winsys so currently this is only available when building Cogl as part
of Clutter.
This tries to make the naming style of files under cogl/winsys/
consistent with other cogl source files. In particular private header
files didn't have a '-private' infix.
