logging: Added locking in flush() and close() handler methods. Thanks to Fayaz Yusuf Khan for the suggestion.

Patch by Francisco Martín Brugué

Closes #8033.

Fix obscure failures of datetime-related tests due to the datetime tests failing to restore the system state completely after testing the pure-Python versions.

Remove setting hash seed to regrtest's random seed and re-execv()ing: this doesn't preserve Python flags and fails from a temp directory.

Remove setting hash seed to regrtest's random seed and re-execv()ing: this doesn't preserve Python flags and fails from a temp directory.

Fix "sys.path modified" warning in test_strlit, by not replacing sys.path itself, only its contents.