gitweb: Make possible to run under mod_perl without ParseHeaders
Add mod_perl version of http_header, setting headers directly (both
for mod_perl 2.0 and 1.0); bits of code taken from CGI and CGI::Util
modules. While at it add cache validation via $r->meets_conditions()
in mod_perl code.
Separate HTTP redirection into http_redirect subroutine and add
mod_perl version, setting headers directly.
All this is meant to allow gitweb to run under ModPerl::Registry (for
mod_perl 2.0) / Apache::Registry (for mod_perl 1.0) without need for
Apache to parse headers (without ParseHeaders), which should speed up
gitweb a bit.
Signed-off-by: Jakub Narebski <jnareb@gmail.com>