Feature/mongo 2.6.5 expressions field path

Most of the tests' diffs are just whitespace (converted spaces to tabs). The only new test is testNestedBelowMissing(), and the addDependencies test was updated to use DepsTracker instead of the old dependencies format. The addDependencies function itself was, as well.

Everything else seemed to be unchanged from 2.5.4 to 2.6.5.