ds: use WNOHANG with waitpid if inside event loop

ds: use WNOHANG with waitpid if inside event loop

While we're usually not stuck waiting on waitpid after
seeing a pipe EOF or even triggering SIGPIPE in the process
(e.g. git-http-backend) we're reading from, it MAY happen
and we should be careful to never hang the daemon process
on waitpid calls.

v2: use "eq" for string comparison against 'DEFAULT'