The U flag is no more used (but still accepted for backward compatibility).

Update the doc. Refactor also related tests.

The _tkinter module loads the Tcl library which creates a thread waiting events
in select(). This thread receives signals blocked by all other threads. We
cannot test blocked signals if the _tkinter module is loaded.

Patch by Bryce Verdier.

Patch by Bryce Verdier.

Patch by Bryce Verdier.

free()d memory arenas on glibc-based systems.  Patch by Charles-François
Natali.

The problem is not specific to Mac OS X.

called. The test checks that SIG_UNBLOCK calls immediatly the signal handler of
the pending SIGUSR1. Improve also the tests using an exception (division by
zero) instead of a flag (a function attribute).

Disable faulthandler timeout thread on Mac OS X: it interacts with
pthread_sigmask() tests.

Patch by Victor Stinner.