Check if expected x'40' characters at end of 1014 blocks

[adelosa]

When unblocking a file, check the blocking characters to make sure they are x'40' otherwise throw a log warning. This is an indication that the file is not blocked correctly and will likely result in an error processing the file. Don't want to throw exception until I have some view as to what characters could actually be there.
Suggest that the user try using the flag to disable block file processing - see #26

[adelosa]

Warning added to block function.