gitweb: Move evaluate_gitweb_config out of run_request

gitweb: Move evaluate_gitweb_config out of run_request

Move evaluate_gitweb_config() and evaluate_git_version() out of
run_request() to run(), making them not run one for each request.
This changes how git behaves in FastCGI case.

This change makes it impossible to have config which changes with
request, but I don't think anyone relied on such (hidden action)
behavior.

While at it, reset timer and number of git commands at beginning of
run_request() in new reset_timer() subroutine.  This fixes case when
gitweb was run using FastCGI interface: time is reported for request,
and not for single run of gitweb script.  This changes slightly
behavior in non-FastCGI case: the number of git commands reported is
1 less (running `git --version` one per gitweb is not counted now).

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>