Fix rules.mk checking SONGBIRD_NIGHTLY for extension versioning
gstmozilla: Move the plugin to be in the components/mediacore/gstreamer tree
gstmozilla: Build the plugin for both bundled and system gst
gstmozilla: preprocess gst_libs file and add gstmozilla plugin to list
gstmozilla: preprocess gst_libs_macosx.txt file, add gstmozilla plugin to list

Need to double check the plugin name on debug builds
gstmozilla: preprocess gst_libs_windows.txt file, add gstmozilla plugin to list

TODO: Make sure that preprocessing gst_libs_windows.txt fixes the need for the perl substitution in the Makefile. There is no ogg.dll in the list, only ogg-0.dll, so I suspect that substitution isn't needed right now anyways...