Clear side bits from value before using it.
Clear side bits from value before using it.

svn path=/trunk/libcss/; revision=6160

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