http_caldav.c: maek sure open ended free-busy query uses UTC at endpoint(s)
http_caldav.c: remove some debugging syslogs
httpd.c: allow static content to be proxied from another server
httpd.c: don't destroy query string when parsing (breaks proxying)
Makefile.in: need to link in libicu wherever libical is used
Moved stuff from httpd.c and http_proxy.c into new http_client.c to be used by HTTP client-side utilities