Mark Ellzey added a function libevent_shutdown() which calls a set of
private functions:
* event_free_globals()
* event_free_debug_globals()
* event_free_debug_globals_locks()
* event_free_evsig_globals()
* evsig_free_globals()
* evsig_free_globals_locks()
* evutil_free_globals()
* evutil_free_secure_rng_globals()
* evutil_free_secure_rng_globals_lock()
Nick tweaked this libevent global shutdown code:
- rename the function to emphasize that it's for global resources
- write more in the doxygen
- make function brace style consistent
- add a missing void in a function definition.