Fix some bytes/str conversion issue

[hexchain]

The output of the keychain password hash has been broken because using a bytes object for %s produces repr-type output. This PR fixes that.

Also, export file names were all numbers because bytes[n] is an int and str(bytes[n]) is just the integer converted to a string. Since we expect PrintNames to always be a bytes object, we should be able to use decode and ignore errors.