The github gitignore defaults for a Python project are odd
Disable wonky test for the moment

Timing issues causing the refresh test to fail intermittently.  Disable for
the moment.
Another quick test
Tidying of list handling

Most importantly:

  - Hooray inheritance!  Switch back to the inheritance model and stop
    bothering to short circuit for digest256

Also starring:

  - add_prefixes should be defined first
  - move a comment from lookup_prefixes to add_prefixes
  - document the format of the return value of lookup_prefixes
  - use temp variables to clean up readability in lookup_prefixes
Somehow managed to delete list_chunks()

Put it back with its test
Whitespace parsing corrections
Test with a slightly more complex data file
Whoops.  Forgot the add the data file
Quick script for generating a data file
Centralize one test function

Move filesystem path handling into tests.base
Tweak the lists delta function so it matches fetch

Also add a simple test for delta.  I'm pretty sure that simple set math isn't
going to cut it in the long run, though.