Revert "Fixed the crashing bug https://github.com/couchbaselabs/TouchDB-iOS/issues/266"

This reverts commit 85d27611e08516e318e368ced3c3406c86a28f28.
Revert "Continued attempt to fix https://github.com/couchbaselabs/TouchDB-iOS/issues/266: TDHTTPResponse -cleanUp should rstop the router from observing notifications. Q: is this a good way to fix - should cleanUp instead set _router to nil or call its -stopNow which does the same, also in a synchronized way?"

This reverts commit 56aea02546b5fb18fa36dae77ba89221883febf6.
Another attempted fix to #266, by retaining self in -dbChanged: such that the roouter doesn't get deallocated during it, as suggested by @snej in https://github.com/couchbaselabs/TouchDB-iOS/issues/266#issuecomment-19927084
Merge branch 'master' of github.com:mz2/TouchDB-iOS into mainline