use short names in comittype

Use mtn for monontone and hg for mercurial. The long names cause ugly
formatting in recentchanges, which has CSS that only allows a few
characters for the commit type column.

IkiWiki/Plugin/mercurial.pm

@@ -217,7 +217,7 @@ sub rcs_recentchanges ($) {
 		push @ret, {
 			rev        => $info->{"changeset"},
 			user       => $user,
-			committype => "mercurial",
+			committype => "hg",
 			when       => str2time($info->{"date"}),
 			message    => [@message],
 			pages      => [@pages],

IkiWiki/Plugin/monotone.pm

@@ -559,7 +559,7 @@ sub rcs_recentchanges ($) {
 					if ($cert->{key} eq $config{mtnkey}) {
 						$committype = "web";
 					} else {
-						$committype = "monotone";
+						$committype = "mtn";
 					}
 				} elsif ($cert->{name} eq "date") {
 					$when = str2time($cert->{value}, 'UTC');