Complete issue #71 and #181

- Make ChangeTracker support POST requests

- Puller’s ChangeTracker uses POST requests when sync gateway version
    is 0.93+
Fixed 3 Replication tests.

Fixed TestAllLeafRevisionsArePushed, TestHeaders, and TestPusherDeletedDoc.

Some key exceptions were getting swallowed,
which prevented TestHeaders from firing
the Changes callback.

Removed the early instantiation of the shared
instance of Manager, which is only used in
the Android simple demo.

Also removed some opportunities for the TaskScheduler to deadlock.
Fixed additional tests.

Allowed broader use of inlining in the TaskScheduler,
and resolved a dispose issue in the MockHttpClientFactory
that lead to a deadlock.

Fixes TestRemoteConflictResolution and TestPuller.
Merge pull request #238 from couchbaselabs/issue-181

Complete issue #71 and #181