Add check_head_headers.sh to verify that all files modified between
develop and HEAD have up to date licenses.
Bug 740326 - Fix over-long log tag. all credit,r=nalexander
Bug 740637 - Part 0: cleanup in SyncClientsEngineStage.
Bug 740637 - Part 1: catch exceptions in InfoCollections background thread.
Bug 740637 - Part 2: always shut down the HTTP cleaner thread.
Bug 740637 - Better handling of unexpected failures during info/collections fetch. r=liuche,nalexander
Merge pull request #133 from mozilla-services/nalexander/check_head_headers

Add check_head_headers.sh to verify that all files modified between develop and HEAD have up to date licenses.
Bug 741165 - Correct SyncResponse.jsonBody.
Bug 741278 - Additional strings for Sync credential validation. r=strings-only
Fix strings in previous commit.
Bug 715794 Part 1 - Adjust syncResult delay to implement client-count-based sync interval.
Bug 715794 Part 2 - Tests.
Bug 741165 - Correct SyncResponse.jsonBody. r=msamuel
Bug 738515 - Null credentials in setup. r=rnewman
Bug 738515 - Review comments.
Bug 738515 - Null credentials in setup. r=rnewman
Bug 740247 Part 1 - Restore ifUnmodifiedSince().
Bug 740247 Part 2 - Small fixes.
Bug 740247 Part 3 - Reset local timestamp on download.
Bug 740247 Part 4 - Use body instead of header timestamp.