Fixes bucketOverrides mechanism
Updates podspec
Issue #267: Prevents early SPBucket init
Issue #271: [SPWebSocketInterface resetHeartbeatTimer] crash
Transform local ADD diff into REPLACE

When both the local and remote diff are additions to a nil value,
the diff transform code drops the local diff in favour of the remote
diff. This commit replaces the previous remote diff with the new local
diff so that each key is transformed consistently.
Merge remote-tracking branch 'upstream/develop' into embedded-objects