failureExitCode should return higher number than 1 if user tries to lock an already locked file

[graysky2]

It would be helpful for scripts, if fscrypt would return an exit code other than 1 if the user triggers an ErrDirAlreadyLocked condition. Use case is for scripting actions. Can you change it to return an error code of 2 for example in the scenario of trying to lock a file that is already locked?