Use int_compare, not seq_if_in, to find if a stream is between 0 and 15.

This makes use of the new ability to write int_compare:n { 0 <= #1 <= 15 }.
The integer test is about the same speed as the earlier seq_if_in, but avoids
the need to declare two constant sequences.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4446 de43f980-851b-0410-b2f7-c40aca1f87e0