SERVER-7379 re-enable tests in shard_key_immutable.js
SERVER-12786: add shell writeMode option
SERVER-12915 update must keep track of updated locs even w/in-place updates
SERVER-12825 don't use ixisect if a compound index is available
SERVER-10026 don't add a collscan solution if ixscan soln exists
Merge remote-tracking branch 'upstream/master'