Fixed bug #68583 Crash in timeout thread

This replaces the GUI element used for execution timeout handling
on Windows. Instead a timer queue technique is used, which is indeed
a thread pool. A timer queue timer is a lightweight object handled
but that thread pool and the timer thread spends most of the time
sleeping and waiting for an alert.

Please note also that this introduces neither binary nor source
breach. The custom timeout thread functions are deleted, however
they was not exported throug DLL, so couldn't be used by any
external code. As well they couldn't be used anywhere in the core
except in executor api, because those custom timeout thread
functions they used to operate on static variables which would
be overwritten (and that would blow).

So instead a relatively modern technique is used for the timeout
handling. It's still not perfect because the executor still has to
check EX(timed_out). This can be a topic for an improvement in
master. But brobably can be tricky as currently it seems to be not
possible to signal an individual thread. Also note another issue
that static variables aren't thread safe, but the current timer
implementation is.