[v3] Change std::hash from FNV to Murmur

[Paolo Carlini <paolo dot carlini at oracle dot com>]

Hi,

the below, contributed by Matt Austern, changes std::hash to use a
different algorithm, a so-called Murmur hash, which in all our
experiments both performs better (eg, on my i7 machine, 2M 71 bytes
strings from about 0.3 secs to 0.2, true both for 64-bit and 32-bit code
generation) and appears of higher quality according to various metrics
(testcases will follow). I'm going to apply it momentarily, I just
tested it again on x86_64-linux multilib. Note that for backward
compatibility we are leaving alone std::tr1::hash.

Paolo.

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