turns out that text is default, and windows hates it if I open a binary file without 'b'
standardize on using join_path to create filenames
(use backslash on windows, even though fopen doesn't seem to care).
this should make future debugging sessions easier, telling us what bugs were or were not fixed at the time of an incident.
added a test to make sure data file can be read/written, and at a minimum, sets global data-version.
also clean up test framework a bit, and introduce a helpful macro.
