Do not use /bin/sh to create child processes.

Instead directly call execvp(). This change is needed for the
soon-to-be-added signal handlers because the /bin/sh parent process does not
pass all signals to it's children, particularly SIGUSR1 on Linux.

The parameters of createChildProcess had to be changed slightly.
utils.exec() also has a changed implementation. A bug involving quoted
arguments was knowingly introduced into utils.exec(). Will fix later.