PATCH RFA: Handle erasing a reference to an entry in a hash table

[Paolo Carlini]

Hi Ian,
> PR 25896 is about a problem when passing a reference to an entry in a
> hash table to the erase function.  The issue was fixed in the TR1
> classes unordered_map and friends.  This patch extends the fix to
> hash_map and friends.
>
> Tested by building libstdc++-v3 and running the C++ and libstdc++-v3
> testsuite on i686-pc-linux-gnu.  The patch includes a couple of tests
> copied from the tests included with the fix for PR 25896.
>
> OK to commit?
>   
Yes, it's ok. I'm not sure you need to mention 2007 among the Copyright
years of the testcases: after all, you adapted the tests from the
existing ones for the unordered containers, but the files are new...

Thanks,
Paolo.