Changes the libutil nudge code to use NtCreateThreadEx on Win8+.
For a test, enables the client.nudge_test test, part of i#120: enable .runall tests on Windows. Here I added a new app win32.infloop to parallel linux.infloop, rather than launching calc.exe or notepad.exe like we did in the past (not yet tackling systemwide injection here). It has a MessageBox with a title containing the pid, allowing us to use tools/closewnd with a unique target name for a clean and race-free exit. win32.infloop also has a 3-minute timeout to avoid leaving stale processes behind in case of issues closing it externally.
Revamped runall.cmake to work on Windows, using "ping" to sleep, updating nudge and close commands, removing stale pid files, etc.
Ported suite code to use run_in_bg on Windows as well as Linux, but with the pidfile coming from drrun.
Fixes #1309 (closed) Fixes #1432 (closed) Issue: #120, #1835 (closed)