Update ocaml-pcre to version 7.1.1
Fix x11 include and lib parameters for configure script.
Make x11 optionnal for ocaml
gstreamer: update to 1.4.0
gst-plugins-base: update to 1.4.0
gst-plugins-good: update to 1.4.0
gst-plugins-bad: update to 1.4.0
gst-plugins-ugly: update to 1.4.0
gst-libav: update to 1.4.0
ocaml: fix x11 include and lib parameters for configure script

Close #2923, fixes #2922.
Merge master into PR

Conflicts:
	pkgs/development/compilers/ocaml/4.01.0.nix
ocaml: refactor the useX11 check to actually work
merge #3330: ocaml: optionalize useX11, update -pcre
merge #3342: update gstreamer to 1.4.0
gst_1 base plugins: enableParallelBuilding

This package seems to be quite a bottleneck otherwise.
gst_1 python: bugfix update
gst-1 gnonlin and editing-services: maintenance update
gstreamer: update to 1.4.0, along with other bumps
webkitgtk: minor update
get xorg/x11 working on Darwin