[v3 patch] Implement N3421 - make functors greater<>

[Jonathan Wakely <jwakely dot gcc at gmail dot com>]

This implements another piece of the C++14 library, STL's "transparent
functors" proposal.  I also added the is_transparent typedefs, which
come from another proposal but modify these "diamond operators".  I
hope to get round to using those typedefs to implement Joaquin's
heterogeneous lookup soon.

2013-11-01  Jonathan Wakely  <jwakely.gcc@gmail.com>

        N3421 C++1y Transparent functors
        * include/bits/stl_function.h (plus<void>, minus<void>,
        multiplies<void>, divides<void>, modulus<void>, negate<void>,
        equal_to<void>, not_equal_to<void>, greater<void>, less<void>,
        greater_equal<void>, less_equal<void>, logical_and<void>,
        logical_or<void>, logical_not<void>, bit_and<void>, bit_or<void>,
        bit_xor<void>, bit_not<void>): Define.
        * doc/xml/manual/status_cxx2014.xml: Update.
        * testsuite/20_util/function_objects/comparisons_void.cc: New.

Tested x86_64-linux, committed to trunk.

Attachment: patch.txt
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