gitweb: may $my_uri and $home_link assignments work for FCGI

gitweb: may $my_uri and $home_link assignments work for FCGI

If the GITWEB_CONFIG set either $my_uri or $home_link then
capture that and force those settings to be in effect immediately
after running evaluate_uri.

This makes it so setting $per_request_config = 0 and running
in FCGI mode just works even if GITWEB_CONFIG needs to set $my_uri
and/or $home_link.

This is a much better arrangement.  If GITWEB_CONFIG is run again
($per_request_config is not false) then that code is still free
to change $my_uri and/or $home_link as the force setting happens
after evaluate_uri but before the additional $per_request_config
call.

So this is the best of both worlds.  Just add:

  our $per_request_config = 0;
  our $auto_fcgi = 1;

to GITWEB_CONFIG and FCGI mode will just automatically work without
the extra overhead of needing to run GITWEB_CONFIG on every request!

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>