Switch from AF_UNIX to UDP on localhost.

Dart does not support AF_UNIX sockets. There is a CL
which would add it, but it was never integrated.
Switch to UDP sockets, bound to localhost.

Also correct several signedness bugs, read() and recv()
return negative numbers on error.

Change-Id: Ib350c7d7459a12c4db20ca992c68e54da7756c7b
5 files changed