Documentation and context restoration on error
Documentation and context restoration on error

svn path=/trunk/libcss/; revision=7996

servo/libcss,prepare/netsurf_libcss,prepare/netsurf_libcss,zhuyadong/libcss,prepare/netsurf_libcss,servo/libcss,servo/libcss,zhuyadong/libcss,zhuyadong/libcss