Merge branch 'oplog-selector-modifier-operators' into devel

Brings optimizations to the oplog-tailing:
- analyze modifications coming from oplog and skip uneccessary fetches for certain $-operators
  + ranges of numbers { $gt: 5, $lt: 33 }
  + inequlities { $not: 5 } or { $nin: [ 1, 3, 4 ] } for scalars
  + equalities { $in: [ 2, 4, 6 ] } for scalars
Refactor matchingDocument into separate method on Matcher's prototype, cache it.
Initialize Matcher._matchingDocument in the constructor.

To declare it explicitly to humans and JITs.