Merge HTCP enhancements.

Changes include:

- Ability to send HTCP CLR requests when objects are invalidated or purged from
 the cache.
- Config logic to allow the following:
	- HTCP peers who ONLY receive CLR messages from us.
	- HTCP peers who NEVER receive CLR messages from us.
	- HTCP peers who NEVER receive CLR messages from us for PURGE requests.
	- HTCP peers who are forwarded CLR messages we receive.