http_helpers: print correct date despite timezone of current system

--HG--
extra : rebase_source : 44315bf58faba771abb1e264ffdf010daf77a919
build system: remove redundancy for defining http server dependencies
http_server_test_main: update http_server_test_main.c to build against newer http_server API
util_fs: fix memory-leak in reparent_path()

--HG--
extra : amend_source : fb4b1b24630f5cd91166e3e9481883e83a45e47b
http_server: improve error handling when accepting new request
util: add davfuse_util_asprintf() function
webdav_server: move verification of tag name to be after verification of the tag's attributes, this is because is_valid_element() relies on is_valid_attribute being called for each attribute