Added bug collisions to bcrypt

[Sc00bz]

Signed char bug: $2y$ is using the correct code. The $2x$ (the old $2a$) extended the sign bit of a character on top of at most the 3 characters before it (4 byte boundary).

Null char bug: nothing after the first null character is used. This breaks when using prehashed bcrypt with raw output.

[lodee77]

1. @ok