gitweb: href(..., -path_info => 0|1)

gitweb: href(..., -path_info => 0|1)

If named boolean option -path_info is passed to href() subroutine, it
would use its value to decide whether to generate path_info URL form.
If this option is not passed, href() queries 'pathinfo' feature to
check whether to generate path_info URL (if generating path_info link
is possible at all).

href(-replay=>1, -path_info=>0) is meant to be used to generate a key
for caching gitweb output; alternate solution would be to use freeze()
from Storable (core module) on %input_params hash (or its reference),
e.g.:
  $key = freeze \%input_params;
or other serialization of %input_params.

While at it document extra options/flags to href().

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Acked-by: Petr Baudis <pasky@suse.cz>
Signed-off-by: Junio C Hamano <gitster@pobox.com>