Finished testcases reorganization and CPU time limit implementation We now have: * Win32-specific code in the win32 module (including bug fixes), * UNIX-specific and generic code in the unix module, * a much cleaner testcases module, * wait4-based resource limits working on Python 3 (this is a bug fix), * no warning/error reported on non-Win32 when -x is not passed but standard input does not come from a terminal, * the maxtime configuration variable replaced with two new variables named maxcputime and maxwalltime, * CPU time reported if it can be determined unless an error occurs sooner than it is determined (e. g. if the wall-clock time limit is exceeded), * memory limits enforced even if Upreckon's forking already breaks them, * CPU time limits and private virtual memory limits honoured on Win32, * CPU time limits honoured on UNIX(-like) platforms supporting wait4 or getrusage, * address space limits honoured on UNIX(-like) platforms supporting setrlimit with RLIMIT_AS/RLIMIT_VMEM, * resident set size limits honoured on UNIX(-like) platforms supporting wait4.