TDReplicator keeps track of what server type it's talking to

Specifically it remembers the "Server:" response header.
This can be used to conditionally use REST API extensions that only some servers support.

Conflicts:
	Source/CBLRemoteRequest.h
	Source/CBL_Replicator.h
	Source/CBL_Replicator.m
_bulk_get implementation

Calling nonstandard REST API that speeds up pull replications.
Only used with compatible servers, i.e. Sync Gateway for now.
https://github.com/couchbase/sync_gateway/wiki/Bulk-GET
Fixes #45.
Save some memory while pulling

Toss out the parsed NSDictionary form of CBL_Revisions that have been pulled and
are waiting to be inserted into the db, leaving only the JSON.
Fix unit tests on iOS (wrong constant for M_PI)