WIP - initial impl of $setOnInsert
> tests for (_.x setOnInsert None) will follow

refs #92
$setOnInsert - removed Opt version of setOnInsert
makes no sense in this context - we can not perform an $unset at "setOnInsert" anyway, since
the document will be fresh - nothing to unset.

refs #92
remove not used syntax
fix test to make the independent on groupBy ordering guarantees
See https://github.com/foursquare/rogue/pull/93 for detailed explanation
why this failed on 2.10 before, but not on 2.9

refs #93
Merge pull request #93 from ktoso/master

Implemented $setOnInsert (mongo 2.4+)