Missing input directory for CSV toolchains results in core dump; --checkconfig message is misleading

[mjordan]

If the directory specified in [FILE_GETTER] input_directory is does not exist, running MIK results in a segmentation fault/core dump. Running --checkconfig prior to running MIK doesn't catch this, since it states:

The path /tmp/bookocr (defined in configuration setting input_directory) does not exist but will be created for you.

--checkconfig should indicate that MIK can't proceed without the input directory, and MIK itself should probably thow an exception and exit with 1 if the input directory (or in fact any file or directory that is not created by MIK, such as the mappings files) is missing.