Tests for duperemove.

This is all pretty basic, mostly we can automatically test for program failure. Ultimately we'll want to parse program output too so we can check very specific conditions.

To run:

1. make
2. cp config.sample config
3. edit config to match your environment
4. run tests/smoke_test.sh and the other tests/test_*.sh files

To create data for your own testing, see src/mkzeros.c and src/gen_mkzeros_test_data.sh.

There are also pre-populated hashfiles in the hashfiles/ directory for testing with --read-hashes.