More tests for both the GMP and the BcMath adapter's
bitwise methods
Fixing some bugs found by the BcMath tests
Fixed some weird results occurring in the BcMath
adapter bitwise methods that were found with the more extensive tests
Yay!

Also, added new methods to support the new logic and keep it DRY:
- isNegative()
- twosComplement()
- flipBits()