gitweb: Add generic git_object subroutine to display object of any type

gitweb: Add generic git_object subroutine to display object of any type

Add generic "object" view implemented in git_object subroutine, which is
used to display object of any type; to be more exact it redirects to the
view of correct type: "blob", "tree", "commit" or "tag".  To identify object
you have to provide either hash (identifier of an object), or (in the case of
tree and blob objects) hash of commit object (hash_base) and path (file_name).

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>