gitweb: minimally fix "fork" support.

gitweb: minimally fix "fork" support.

A forked project is defined to be $projname/$forkname.git for
$projname.git; the code did not check this correctly and mistook
$projname/.git to be a fork of itself.  This minimally fixes the
breakage.

Also forks were not checked when index.aux file was in use.
Listing the forked ones in index.aux would show them also on the
toplevel index which may go against the hierarchical nature of
forks, but again this is a minimal fix to whip it in a better
shape suitable to be in the 'master' branch.

Signed-off-by: Junio C Hamano <junkio@cox.net>