Nix daemon: respect build timeout from the client
nix-build: Respect --timeout
Show that --timeout doesn't work if the build produces log output
Fix --timeout

I'm not sure if it has ever worked correctly.  The line "lastWait =
after;" seems to mean that the timer was reset every time a build
produced log output.

Note that the timeout is now per build, as documented ("the maximum
number of seconds that a builder can run").