#249 tweak behaviour so all fields prefixed; begin refactoring transform tests
#267 factor out petl.test.transform.test_conversions
#267 factor out petl.test.transform.test_dedup
#267 factor out petl.test.transform.test_fills
#267 factor out petl.test.transform.test_headers
#267 factor out petl.test.transform.test_maps
#267 factor out petl.test.transform.test_reductions
#267 factor out petl.test.transform.test_regex
#267 factor out petl.test.transform.test_reshape
#267 finish factoring out petl.test.transform