inputhook_qt4: handle KeyboardInterrupt in a way compatible with 'readline'. While the previous code works fine on Windows, on Linux with 'readline' the situation is different: once we disable the Qt4 event loop, we go back waiting in the select() inside readline.c's readline_until_enter_or_signal() function. When that select() is interrupted, the PyOS_InputHook is executed if present and the pending KeyboardInterrupt is delivered as soon as bytecode execution starts, even before entering the `try:` clause! As at that point we're in a ctypes callback, this will lead to an internal error. The only solution is therefore to disable the PyOS_InputHook temporarily.