git-cvsserver: add ability to guess -kb from contents

git-cvsserver: add ability to guess -kb from contents

If "gitcvs.allbinary" is set to "guess", then any file that has
not been explicitly marked as binary or text using the "crlf" attribute
and the "gitcvs.usecrlfattr" config will guess binary based on the contents
of the file.

Signed-off-by: Matthew Ogilvie <mmogilvi_git@miniinfo.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>