gitweb: Put all per-connection code in run() subroutine

gitweb: Put all per-connection code in run() subroutine

All code that is run per-connection (as opposed to those parts of gitweb
code that can be run once) is put into appropriate subroutines:
 - evaluate_uri
 - evaluate_gitweb_config
 - evaluate_git_version (here only because $GIT can be set in config)
 - check_loadavg (as soon as possible; $git_version must be defined)
 - evaluate_query_params (counterpart to evaluate_path_info)
 - evaluate_and_validate_params
 - evaluate_git_dir (requires $project)
 - configure_gitweb_features (@snapshot_fmts, $git_avatar)
 - dispatch (includes setting default $action)

The difference is best viewed with '-w', '--ignore-all-space' option,
because of reindent caused by putting code in subroutines.

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