Updated ObjectExpression to mongo 2.6.5

Changes to ObjectExpression.js to support change to addDependencies(), which accepts a DepsTracker.  This may need to be tested some more after Dependencies.js is updated.

Changes to test/.../ObjectExpression.js to support change to addDependencies().  The first few test cases are now supported, but the majority need to be updated again after more updates are made (paths, etc).

Change to FieldPathExpression.js.  Similar change for addDependencies().
Style note: if (!depsTracker.fields) is functionally equivalent and a bit more brief.