set siginterrupt flag to False

This patch sets the siginterrupt flag to False so that interrupted system calls
are automatically restarted. This notably fixes applications using the Precice
coupling library, which does not currently handle EINTR read errors. This patch
also changes the unit tests to SIGINT-based control, so that signal handlers
are not blocked while waiting for user input.

bottombar.py

@@ -254,6 +254,7 @@ def __init__(self, handler: Callable[[], None]) -> None:
                 if signal.getsignal(sig) != signal.SIG_DFL:
                     raise RuntimeError(f'signal {sig.name} is in use')
                 signal.signal(sig, lambda sig, frame: handler())
+                signal.siginterrupt(sig, False) # restart any interrupted system calls
             signal.setitimer(signal.ITIMER_REAL, 0.)
             _debug('started signal based auto-redraw handler')
         def set(self, refresh: float) -> None:

tests.py

@@ -1,9 +1,20 @@
 import bottombar as bb, os, time
+import signal
+
+def input(msg):
+    print(msg, end='', flush=True)
+    while True:
+        try:
+            signal.pause()
+        except KeyboardInterrupt:
+            break
+    print()
 
 print('\033[{};1H'.format(os.get_terminal_size().lines))
 print('====================')
 print('BOTTOMBAR UNIT TESTS')
 print('--------------------')
+print('PRESS CTRL+C TO PROCEED TO THE NEXT TEST')
 
 print('1. basic terminal tests')
 input('   a. check that this question shows at the very last line')