gitweb: Make .error style generic

Style for td.error was introduced in 1f1ab5f (gitweb: style done with stylesheet, 2006-06-20) to replace inline style for errors in old multi-column "git annotate" based 'blame' view. This view was then since removed (replaced by "git-blame" based 'blame' view, with fewer colums), making this style unused. Make this style more generic by replacing td.error with .error to make it apply to any element. It will be used in 'blame_incremental' view to show error messages. Signed-off-by: Jakub Narebski <jnareb@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>