git-cvsimport: really convert underscores in branch names to dots with -u

The documentation states for the -u option that underscores in tag and
branch names are converted to dots, but this was actually implemented
for the tag names only.

Kurt Roeckx reported this through
 http://bugs.debian.org/446495

Signed-off-by: Gerrit Pape <pape@smarden.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-cvsimport.perl

@@ -818,6 +818,7 @@ while (<CVS>) {
 		$state = 4;
 	} elsif ($state == 4 and s/^Branch:\s+//) {
 		s/\s+$//;
+		tr/_/\./ if ( $opt_u );
 		s/[\/]/$opt_s/g;
 		$branch = $_;
 		$state = 5;