correct example ip
compile with annot files by default
Use explicit command-line flags to pass through the --unix and --xen compiler switches.

This requires the latest OPAM package specifications, and is part 1 of a commit series
force the installation of mirage-unix or mirage-xen depending on the backend
split out util functions
Add a `--socket` flag to activate socket-based networking (UNIX only).
do not make install depend on build to make sudo installations easier
mark 0.9.3