gitweb_config.perl: add a few extra "our" declarations
It's most convenient to be able to load the "gitweb_config.perl"
configuration outside of gitweb.cgi.
Make that easier to accomplish by adding a couple of "our"
declarations for the two hashes (feature and html_cache_actions)
that have values set.
This makes it clear what's supposed to happen when those two
hashes have items set in them and makes it simpler to "use" the
gitweb_config.perl file from a location outside gitweb.cgi.
Signed-off-by: Kyle J. McKay <mackyle@gmail.com>