This commit addresses some of the comments to the previous commit.

In particular:
* the CDTReplication -source: and -target: methods were removed from the base class.
* the -(id) filter: method was removed from CDTReplication
* the CDTReplication -dictionaryForReplicatorDocument was rewritten. The subclasses
are responsible for filling this out.
* CDTPushReplication and CDTPullReplication add the source and target information
to the returned NSDictionary in -dictionaryForReplicatorDocument explicitly.
* the to-be-deprecated methods in CDTReplicatorFactory (-onewaySource...target...)
were rewritten to use the new -oneWay:error method
* NSError reporting was added to -oneWay:
* ReplicationAcceptance test for pull replication was modified to pull specific
docs and to pull a random subset of docs

Still to be discussed is the benefits/drawbacks of adding the properties 'user',
'password', 'host', 'protocol', etc. to the CDTReplication class instead of
(or in conjunction with) setting a NSURL.

When the pull request for this branch is +1, I'll squash the commits
into an appropriate number of commits / messages. I didn't want to rewrite over
previous comments.