Hi

    During a recent discussion on Reflector about max_load_factor some
pointed that libstdc++ has not the constant complexity as imposed by the
Standard in Table 103 because we try to respect the new factor by
potentially rehashing the container. This patch fix this problem by
adopting VS Standard Library behavior of retaining the targeted
max_load_factor and comply to it as soon as possible on insertion.

    * include/bits/hashtable.h (_Hashtable<>::__rehash_policy): Remove
    container rehash.
    * testsuite/23_containers/unordered_set/max_load_factor/robustness.cc:
    Adapt.

Tested under linux x86_64.

Ok to commit ?

François