Win64: set FPU CW to 64-bit, set sprintf output format to 2 digits in ex...

...ponents

This changes the MS C runtime to better match what is done by the other platforms:
- set precision of floating point operations to 64-bit mantissa
- change the number of digits in floating point exponents emitted by sprintf from 3 to 2

There are unittests in phobos that detect the differences, but these are not run under Win64 so far.