gl: add dep on gstegl

Temporary until we merge the two libraries
Revert "gl: add dep on gstegl"

It was already in _LIBADD

This reverts commit b10a3530804335fc3b9494603ef78ce9417c3bc8.
gl: add path of the gstegl library

Temporary until we merge the two libraries
gl: add the option of disabling cocoa on OS X using --disable-cocoa
gl: only link against gstegl if we are using egl

Assuming if we are building egl that the egl library is built
gl: add GModule libs for win32
gl: allow not building the gl library plugins
gl: set default value to 0 for all definitions that go to gstglconfig.h

To avoid warnings like "GST_GL_HAVE_OPENGL is not defined".
As we are using #if instead of #ifdef
gl: check for X unconditionally

Without this the HAVE_X macro is empty, not "no" or "yes", which is not
what the later code is counting on.

https://bugzilla.gnome.org/show_bug.cgi?id=726591
gl: fix the use of always-defined macros

After 2a0f0399ae226089c2ba07b1b904741b856f37af GST_GL_* macros are always
defined to 0 or 1. Don't use #ifdef ... or #if defined() on them.

https://bugzilla.gnome.org/show_bug.cgi?id=726591
gl: don't default to GST_GL_HAVE_WINDOW_DISPMANX=1

Mistake introduced by 2a0f0399ae226089c2ba07b1b904741b856f37af

https://bugzilla.gnome.org/show_bug.cgi?id=726591
dvbsuboverlay: Don't forward text gap events downstream

That gap is only for the subtitle stream and not for the video stream.
gl: keep only one occurence of '#include <EGL/egl.h>'

To simply maintainance if we need to put specific includes around it.
gl: silence warnings building for RPI related to 'vcos_*'

Similar than 1190a79b199584cfc4dd62c474531c32cfbba425
gl: silence a critical if upstream does not provide us with meta params
gl/mixer: fix download check for failure
gl: use wglCreateContextAttribsARB to create share context

https://bugzilla.gnome.org/show_bug.cgi?id=726494
check: fix make check

The mpeg parser now flags the stream as mpeg2 if there is a picture
extension header, so remove it for mpeg1 data.
gl/win32: use the correct include and gst-indent
gl: reorganize the extension headers by function rather than api