The default value of @mergerx uses \W, which matches a non-word
character; this means that commit messages like "Merging FOO" are not
matched by default; using \b, which matches a word boundary, instead of
\W fixes that.

This change was suggested by Frédéric Brière through
 http://bugs.debian.org/463468Signed-off-by: NGerrit Pape <pape@smarden.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>