gitweb: Fix handling of whitespace in generated links

When creating path_info part of link, don't encode space as '+', because
while $cgi->param('foo') translates '+' in query param to ' ', neither
$ENV{'PATH_INFO'} nor $cgi->path_info() do.

This fixes the issue with pathnames with embedded whitespace and
$feature{'pathinfo'} / path_info links.  It is done by using newly
introduced esc_path_info() instead of esc_url() in href() subroutine.

Also while links are more clear not escaping space (' ') characters in
generated links, the trailing space must be URI-encoded, otherwise would
get discarded.

Issue noticed thanks to John 'Warthog9' Hawley.

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