ForAll / Universal Quantifiers

We have a Not iterator now. It'd be possible to add a shorthand macro in Gremlin to emulate the [Universal Quantifier](http://en.wikipedia.org/wiki/Universal_quantification), ForAll.

All queries currently work on existence. That is, each stage depends on "there exists some path X to node Y". Using negation you can achieve "for all paths from X, (rest of query holds)".

The key insight being that
`(X holds for (ForAll A)) == (X holds for A) AND (X holds for (Not (Not A))) == (X holds for (A AND (Not (Not A))))`

In today's parlance, this is:
var a = g.M()....
`g.V().And(a).And(g.V().Except(g.V().Except(a)))...`

It's a hack, but one that holds mathematically. Currently can be implemented as a macro on the query level, and is actually really hard to optimize further. (Suggestions, of course, are welcome)

Start with the existing Not iterator and the query-level Gremlin macro described here. Compare the proposed ForAll behavior with the supplied And/Except/Not expression; done means a supported universal-quantifier shorthand with equivalent results, while optimization remains unresolved.

Written by the indexing model from the issue text.