Reduce line number bloat, fix hover effect

Currently line numbers look like (for blob view and sdiff respectively):

    <a class='no' id='n68' name='n68' href='#n68'>68</a>
    <td class='lineno'><a class='no' href='...#n1' id='n1' name='n1'>1</a></td>

name=".." is unnecessary if the id attribute is set (this even applies
to IE6), so drop it. (aside, in HTML5, the name attribute is gone.)

The line number links can be selected through their parent classes, no
need for another class "no", so drop it too.

For a file with 2000 lines, this yields a saving of 40% (29% gzipped).

While at it, fix the hover effect of line numbers: now the line number
get a black background as was intended.

Signed-off-by: Peter Wu <lekensteyn@gmail.com>
Signed-off-by: Lukas Fleischer <cgit@cryptocrack.de>