Yet another attempt at OOB handling in the network abstraction. This

Yet another attempt at OOB handling in the network abstraction. This
version allows you to specify, per socket, which sockets receive OOB
data in-line (so that you know what was before the mark and what was
after) and which receive it out of line (so it's really a one-byte
out-of-band facility rather than discard-to-mark). This reflects the
fact that rlogin appears to make more sense in the latter mode, and
telnet in the former. This patch makes rlogin work right for me.

[originally from svn r921]