First half (set/multiset) of N3657

[Howard Hinnant]

On Aug 12, 2013, at 2:06 PM, Marshall Clow <mclow.lists at gmail.com> wrote:

> Adding Heterogenous comparison lookups to associative containers.
> 
> In this patch:
> * Marking the comparison functions as transparent (thanks Zhihao!)
> * Updating the synopsis in <set>
> * Defining the four template functions (find, equal_range, upper_bound, and lower_bound) in set/multiset
> * enable_if-ing them for transparent comparison functions.
> * added a utility class named "PrivateConstructor" to test these things.
> * Tests. Lots of guns - I mean tests.
> 
> Howard has already suggested an enhancement to the enable if to deal with the case where there's an implicit conversion from the key type being passed to find() and the key type of the container. This should work in C++11, and it would be nice if it continued to work.
> 
> Still to do: map and multi-map.

Looks good to me, except multiset/equal_range.pass.cpp has tabs, and some commented out tests that should be uncommented.  Please commit with these changes.

Thanks,
Howard