Quote git config output for nonstop mode check
Respect nonstop mode even when there's no recorded work
Move non-stop mode flag to .git/WORK_NONSTOP

Was in .git/config, but it's rather a frequently changing flag.
Add command 'nonstop'
Make 'nonstop {on,off}' less verbose
Respect configuration variable work.minTime

So that minimal record time can be specified in config instead of the
default 1 minute.