Changes to date and time expression classes
Add DateToStringExpression.js
EAGLESIX-2706 expression Compare ported to mongo 2.6.5
EAGLESIX-2708 expression Subtract ported to mongo 2.6.5
Merge branch 'feature/mongo_2.6.5_expressions' into feature/mongo_2.6.5_expressions_Date
Added DateToString.js and started the test cases module
Added a few DateToString test case skeletons
Merge branch 'feature/mongo_2.6.5_expressions' into feature/mongo_2.6.5_expressions_Date
EAGLESIX-727 Expressions: Date-related expression comments, finish DateToString
Merge branch 'feature/mongo_2.6.5_expressions' into feature/mongo_2.6.5_expressions_Date
EAGLESIX-727 Expressions... DateToString.  evaluateInternal() change to return a null for null input
EAGLESIX- filling out the test cases, minor changes to expression classes.
EAGLESIX-2699 This includes ifNull, Not, and Cond.  The latter is turning out to be interesting - I am not sure the code we have works at all.
EAGLESIX-2699 Filled out test cases for 'object' implementation of $cond.
EAGLESIX-2699 more enhancements to the $cond code.
EAGLESIX-2696 Added more comments to help me remember what to fix :-P
Merge branch 'feature/mongo_2.6.5_expressions' into feature/mongo_2.6.5_expressions_ifNull_Cond_Not
EAGLESIX-2699 Improved the expression to better match the c++ code.
Support the array and object forms of the expression.
Enhance the test cases to test for exactly 3 args in the array form.
Enhance the test cases to test for arguments being out of order in the object form.
EAGLESIX-2699 Add error codes to error messages.  Add test cases for missing arguments.
EAGLESIX-2699

Merge branch 'feature/mongo_2.6.5_expressions' into feature/mongo_2.6.5_expressions_ifNull_Cond_Not

Conflicts:
	lib/pipeline/expressions/CondExpression.js
	lib/pipeline/expressions/IfNullExpression.js
	lib/pipeline/expressions/NotExpression.js