Formatting
New test case for concurrent reading (threading)
Drop file handlers caching
Small cleanup
Update the 'tailoring atexit hooks' recipe to be compatible with the new FileRegistry
_FileRegistry now inherits from 'object' (see gh-314)
Merge branch 'avalentino-nofilecache' into develop

Conflicts:
	RELEASE_NOTES.txt
	tables/file.py
	tables/tests/test_basics.py