allow numeric font-weight in client-side css sanitizer

font-weight is special because the allowed value list includes things
that look like numbers. The client-side css parser applies numeric value
checks before literal value checks, so font-weight:200 is always elided.

This fixes that by moving the literal value check before the numeric
value check.

This fixes
https://code.google.com/p/google-caja/issues/detail?id=1771

[MikeSamuel, 2013-07-17 22:03:47]

LGTM

[felix8a, 2013-07-17 22:11:24]

@r5497