gitweb: Use light/dark for class names also in 'blame' view

Instead of using "light2" and "dark2" for class names in 'blame' view
(in place of "light" and "dark" classes in other places) to avoid
changing style on hover in 'blame' view while doing it for other views
(like 'shortlog'), use more advanced CSS, relying on the fact that
more specific selector wins.

While at it add a few comments to gitweb CSS file, and consolidate
some repeated info.

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

gitweb/gitweb.css

@@ -226,22 +226,25 @@ th {
 	text-align: left;
 }
 
-tr.light:hover {
-	background-color: #edece6;
-}
-
-tr.dark {
-	background-color: #f6f6f0;
+/* do not change row style on hover for 'blame' view */
+tr.light,
+table.blame .light:hover {
+	background-color: #ffffff;
 }
 
-tr.dark2 {
+tr.dark,
+table.blame .dark:hover {
 	background-color: #f6f6f0;
 }
 
+/* currently both use the same, but it can change */
+tr.light:hover,
 tr.dark:hover {
 	background-color: #edece6;
 }
 
+/* boundary commits in 'blame' view */
+/* and commits without "previous" */
 tr.boundary td.sha1,
 tr.no-previous td.linenr {
 	font-weight: bold;

gitweb/gitweb.perl

@@ -4801,7 +4801,7 @@ sub git_blame {
 	git_print_page_path($file_name, $ftype, $hash_base);
 
 	# page body
-	my @rev_color = qw(light2 dark2);
+	my @rev_color = qw(light dark);
 	my $num_colors = scalar(@rev_color);
 	my $current_color = 0;
 	my %metainfo = ();