git-cvsimport: fix merging with remote parent branch

commit-tree fails when specifying a remote name (via -r option) and
one of the parent branch has a name. Prefixing with "$remote/" fix it.
Signed-off-by: NMarc-Andre Lureau <marcandre.lureau@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-cvsimport.perl

@@ -730,7 +730,7 @@ sub commit {
 		next unless $logmsg =~ $rx && $1;
 		my $mparent = $1 eq 'HEAD' ? $opt_o : $1;
 		if (my $sha1 = get_headref("$remote/$mparent")) {
-			push @commit_args, '-p', $mparent;
+			push @commit_args, '-p', "$remote/$mparent";
 			print "Merge parent branch: $mparent\n" if $opt_v;
 		}
 	}