Moving all our URL and URL pattern parsing code to the same file - it

Moving all our URL and URL pattern parsing code to the same file - it
was scattered around in filters.c, loaders.c and parsers.c.

Providing a single, simple url_match(pattern,url) function - rather than
the 3-line match routine which was repeated all over the place.

Renaming free_url to free_url_spec, since it frees a struct url_spec.

Providing parse_http_url() so that URLs can be parsed without faking a
HTTP request line for parse_http_request() or repeating the parsing
code (both of which were techniques that were actually in use).

Standardizing that struct http_request is used to represent a URL, and
struct url_spec is used to represent a URL pattern.  (Before, URLs were
represented as seperate variables and a partially-filled-in url_spec).