fix for StorageList and tests added

gluon/storage.py
StorageList had a recursion error (please check the implementation before committing)

gluon/tests*
added the fix_path module to avoid those ugly lines at the beginning of each test file
added tests for gluon.contenttype and test_fileutils
added tests for missing Storage methods
Merge pull request #504 from niphlod/fix/storage_and_tests

fix for StorageList and tests added