major revamp of test_decompiler.py

   - changed the test format
   - exposed a nicer interface, especially for test generation
   - removed the *.test files from the repo
   - removed the explicit tmpdir, in favor of Python's tmpdir finder
   - prettied up some of the test outputs
   - made the test inputs explicit with the `test_registry`
clear out pre-existing source files
Add plugin helper functions
Merge remote-tracking branch 'remotes/cjcarey/master'
Change decompiler test script