replace modulus with FastMod
replace modulus with FastMod

Replaces the slow modulo operation with a much faster 32bit multiplication & shift. This works
because the hash should be uniformly distributed between 0 and 2^32-1. This speeds up the benchmark
by a factor of about 1.3:

RollingBloom, 5, 1500000, 3.73733, 4.97569e-07, 4.99002e-07, 4.98372e-07 # before
RollingBloom, 5, 1500000, 2.86842, 3.81630e-07, 3.83730e-07, 3.82473e-07 # FastMod

Be aware that this changes the position of the bits that are toggled, so this should probably
not be used for CBloomFilter which is serialized.

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