- Attempted to fix a problem when Squid ignores all header fields it cannot

- Attempted to fix a problem when Squid ignores all header fields it cannot
  parse.  Now we support a two-level scheme where raw header fields are
  preserved regardless of our parsing/interpretation abilities. Each header
  field has also a "cache" where we store parsed value of the field (if any).
- The only opearation on raw headers left is "joining" of appropriate headers
  together.
- Fixed a lot of minor problems and added new header fields:  Server, X-Cache,
  and other.