gitweb: Harden UTF-8 handling in generated links

esc_html() ensures that its input is properly UTF-8 encoded and marked
as UTF-8 with to_utf8().  Make esc_param() (used for query parameters
in generated URLs), esc_path_info() (for escaping path_info
components) and esc_url() use it too.

This hardens gitweb against errors in UTF-8 handling; because
to_utf8() is idempotent it won't change correct output.

Reported-by: Michael Wagner <accounts@mwagner.org>
Signed-off-by: Jakub Narębski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Merge branch 'jn/gitweb-utf8-in-links' into pu

* jn/gitweb-utf8-in-links:
  gitweb: Harden UTF-8 handling in generated links