Support MDB filenames starting with `--`

[huerlisi]

First off, thanks a lot for this gem:-)

We're using this to build importers for data migration from existing systems to our own dentist software. We therefore see many different filenames, even strange ones;-) One is especially strange as it follows the pattern --XXX.mdb. This one triggers an error when trying to import using this gem as the filename is parsed as options. The tools support using -- as a delimiter between options and the main argument.

Please use -- when calling the mdb- binaries to also support such filenames.

Thanks a lot!