The test-vconn program binds a socket to a nonspecific port number. To
add SSL support to this program, it needs to be able to use SSL, and the
stream library is the easiest way to do that. But the stream library
can't bind to a nonspecific port. This commit adds that feature, by adding
it to the function that the stream SSL library uses as a building block.
SSL, which will be added in an upcoming commit, requires some background
processing, which is best done in a "run" function in our architecture.
This commit adds stream_run() and stream_run_wait() and calls to them from
the places where they will be required.
This code is heavily based on the vconn code. Eventually we should make
the stream-based vconns (currently that's all of them) a wrapper around
streams, but I haven't done that yet.
SSL is not implemented yet.
