Teach log search about --grep, --author and --committer

This makes the log searching more explicit, using a dropdown box to specify
the commit field to match against.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

cgit.css

@@ -144,15 +144,32 @@ td#search form {
 	padding: 0px;
 }
 
-td#search input {
+td#search select {
 	font-size: 9pt;
 	padding: 0px;
-	width: 10em;
 	border: solid 1px #333;
 	color: #333;
 	background-color: #fff;
 }
 
+td#search input {
+	font-size: 9pt;
+	padding: 0px;
+}
+
+td#search input.txt {
+	width: 8em;
+	border: solid 1px #333;
+	color: #333;
+	background-color: #fff;
+}
+
+td#search input.btn {
+	border: solid 1px #333;
+	color: #333;
+	background-color: #ccc;
+}
+
 div#summary {
 	vertical-align: top;
 	margin-bottom: 1em;