Fixed bug on _.memoize.  _.memoize did not work correctly on a a multi-a...

Fixed bug on _.memoize.  _.memoize did not work correctly on a a multi-argument function when a hash was not provided.  Previously, it was only including the first argument into the cache.  The update provides a conditional statement to det
ermine if hasher===_.identity.  If it does, then the appropriate code is applied
 to include the entire arguments array into the cache.
-All tests passed with new implementation
-Previously, a function like var add = function(a,b){return a+b;} if used with m
emoize, var fastAdd = _.memoize(add), fastAdd(2,3) would give the same response
as fastAdd(2,6) or fastAdd(2,7) after fastAdd had been implemented on arguments
where the first values were equal.  The new implementation fixes this issue.