VCheckInterrupt - determines whether to interrupt a process.
int *interrupt; /*RETURN*/
VCheckInterrupt determines whether to interrupt a process by checking if
the least recently queued event is a right button press. If it is,
VCheckInterrupt returns 1, otherwise 0 to *interrupt. VCheckInterrupt
works only when the process is running in the foreground. VSelectEvents
should be called to select ButtonPress event for the related window(s) before
0 - work successfully.
interrupt - returns 0/1 to indicate the interrupt happens.
VCheckInterrupt works only if the process is running in the foreground.
If interrupt is NULL, or VCreateColormap is not called earlier,
VCheckInterrupt prints an error message to the standard error stream,
produces a core dump file and exits from the current process.