Merge branch 'jh/gitweb-caching' (early part)

* 'jh/gitweb-caching' (early part): gitweb: Add optional extra parameter to die_error, for extended explanation gitweb: add a "string" variant of print_sort_th gitweb: add a "string" variant of print_local_time gitweb: Check that $site_header etc. are defined before using them gitweb: Makefile improvements gitweb: Load checking gitweb: Make running t9501 test with '--debug' reliable and usable