aside from the addition of OpenSSL support a few other changes have been included:
- setEngine(), as added by petrich, is depricated (not that it was ever in trunk to begin with)
it has been replaced with isValidEngine() and setPreferredEngine().
- replace _generate_xor() with increment_str()
_increment_str() had extra functionality that wasn't being used. ie. it could concatenate
multiple successive string increments to one another automatically. but not only was that
functionality not used - it also made the function less versatile. _increment_str() can be
used more easily for iterative brute forcing (for example)
- rename Crypt_Base::_stringShift to Crypt_Base::_string_shift (for consistency)
- more expansive unit test coverage
