gitweb: Move call to evaluate_git_version after evaluate_gitweb_config

gitweb: Move call to evaluate_git_version after evaluate_gitweb_config

Now evaluate_git_version() is inside run_request() to be called for each
request, instead of once per starting gitweb; this currently matters only
when using FastCGI interface (gitweb.fcgi).

This change was done because evaluate_git_version() uses $GIT variable,
which can be set / modified by gitweb config file, but the variable is
modified this way by gitweb config file used in gitweb tests.  Without
this change there is spurious extra output from t9500 test when tests are
run with '--debug' option.

Signed-off-by: Jakub Narebski <redacted>
Signed-off-by: Junio C Hamano <redacted>