Unordered container insertion hints

[François Dumont]

Hi

     Here is a patch to consider the hint that users can give to 
enhancement insertion performances. As you can see I only use it for 
unordered_multi* containers to potentially avoid research within the 
bucket nodes.

     Note that I have use a call to _M_equals to avoid a hash code 
computation when we end up inserting after the hint. It is an 
optimization because I consider that _M_equals will be always faster 
than a hash code computation. I think that I will submit an other patch 
later to generalize this when possible to limit the small performance we 
noticed when adopting the new data model (unless performance tests are 
showing me that it is worst).

     I try to document it. If you accept this patch tell me if it is 
with or without the documentation cause I know that my English is not 
good enough. I didn't find out how I can fix the doc URLs regarding 
usage of hints in the std::unordered_* Doxygen comments.

2013-05-20  François Dumont  <fdumont@gcc.gnu.org>

     * include/bits/hashtable_policy.h (_Insert_base): Consider hint in
     insert methods.
     * include/bits/hashtable.h: Likewise.
     * testsuite/23_containers/unordered_multimap/insert/hint.cc: New.
     * doc/xml/manual/containers.xml: Document hitting in unordered
     containers.

François

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