Error code when failed verification

[bicyclesonthemoon]

One of the available commands is "-c", the verification.
If it is successful the return code is 0.
If it fails the return is code is 5.

The problem is that in case of failure there is always the same error code but actually there could be two different situations:

1. It is not possible to perform the verification because for example the microcontroller does not respond or something like this.
2. It is possible to perform the verification but the result is that the memory content does not match the expected hex file.

My proposition is that in case when verification is performed correctly but flash content doesn't match expectation the software should return a different error code than when verification could not be performed.

[bicyclesonthemoon]

I looked back to this topic.
I would be ready to implement this and prepare a pull request.
The only thing left unclear to me is what should be the code?

Currently the returned code is EIO.
Which is ok for the case where it failed to perform the verification.
But I would like to know what is the appropriate error code for the situation where it correctly verified that flash doesn't match.
I looked through the available error codes from errno.h but none seemed appropriate.

If I have the info, which code you would like to see here, I will be ready to prepare a pull request to this.