pyloxi: automatically test all datafiles

The new function add_datafiles_tests is fairly magical but I don't see a better
way to do this in Python 2.6.
loxigen: ignore emacs backup files when searching for input files
test_data: preserve leading whitespace

This is required for the pretty printing tests.
pyloxi: move remaining basic serialization tests to datafiles
Merge pull request #15 from rlane/more-test-data

Move more serialization tests into test_data