Add mod_perl version string (the value of $ENV{'MOD_PERL'} if it is
set) to "generator" meta header.
The purpose of this is to identify version of gitweb, now that
codepath may differ for gitweb run as CGI script, run under
mod_perl 1.0 and run under mod_perl 2.0.
Signed-off-by: Jakub Narebski <jnareb@gmail.com> Signed-off-by: Junio C Hamano <junkio@cox.net>