Rename uint to uint32_t
Modified the "fast mint" procedure in Coin.cpp
While the original is secure, this version requires less
of an argument.
Also modified Benchmark.cpp to increase
the number of coins minted during benchmarking.
Merge pull request #4 from jhasse/mingw

Rename uint to uint32_t
Modified the coin validity checks to ensure that coins are verified immediately
upon deserialization. Added a 'valid' flag to each PublicCoin object, and
an isValid() method to check it. Also changed the Accumulator to check this flag
rather than repeating the validity test unnecessarily.
Finally: wrote a new unit test to test against invalid (non-prime) coins.
Switched all invalid_argument exceptions to be ZerocoinExceptions.
This means we can properly catch them all with a single catch {} block.