fork() can return -1 on error (too many processes, out of memory).
The old code treated pid_ == -1 as a successful fork, entering the
parent branch and calling waitpid(-1, ...) which waits for ANY
child process. Added explicit check: close pipes, free memory,
and return on fork failure.
PIThread::stopAndWait now returns bool
PIKbdListener on Linux now use piwaitevent_p and can immediately stop
new base method piZeroMemory, also migrate all "memset 0" to piZeroMemory
in almost all methods removed timeouts in milliseconds, replaced to PISystemTime
PITimer rewrite, remove internal impl, now only thread implementation, API similar to PIThread
PITimer API no longer pass void*
PIPeer, PIConnection improved stability on reinit and exit
PISystemTime new methods
pisd now exit without hanging