gitweb: Precompile CGI routines for mod_perl

gitweb: Precompile CGI routines for mod_perl

Following advice from CGI(3pm) man page, precompile all CGI routines
for mod_perl, in the BEGIN block.

  If you want to compile without importing use the compile() method
  instead:

    use CGI();
    CGI->compile();

  This is particularly useful in a mod_perl environment, in which you
  might want to precompile all CGI routines in a startup script, and then
  import the functions individually in each mod_perl script.

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