Add bash completion for dmctl.
Merge branch 'master' of github.com:caldwell/daemon-manager
[daemon-manager-completion.bash] POSIX awk has no -e option.
[daemon-manager.cc] Need to include stdlib.
[Makefile] We rely on c++11 features now that they are common.
Use a single command socket for all users.

We now authorize users by using the LOCAL_PEERCRED socket option. This
should be equivalent (security-wise) to the old method of using file system
permissions.

This moves all the socket serving/connecting code out of user.cc and into
daemon-manager.cc (for the server), dmctl.cc (for the client), and
command-sock.cc (for the shared sock_addr stuff).

Closes #2
[daemon-manager.cc] Add support for linux's SO_PEERCRED

Which of course is different from OS X/BSD's for some stupid reason.
Isolate SO_PEERCRED/LOCAL_PEERCRED nastiness to its own file (peercred.cc)