Bug 930718 - Remove reference to Solaris patch in readme. r=cpearce

Forgot this in the original commit.
Bug 930718 - Revert os.h to upstream version. r=cpearce

Forgot to re-run update.sh after removing the Solaris patch.
Bug 931060 - Add encoder files to in-tree libvorbis. r=xiphmont

Add vorbisenc.c and its dependent headers to the libvorbis build
and export the relevant symbols. Based on a patch by Benjamin Chen.