This reverts commit 682bbdfe.

AF42 has both the properties of CS42 and the IMM bit.

Whether this has the advantages or disadvantages of just one or
the other, I don't know. With most mac80211 stacks this will
force mosh packets in the VI queue on wireless.

As for pfifo_fast, have to look it up...

Closes #248.

This reverts commit b0e05776.

This reverts commit 63459ed1.

Closes #265.

For pselect() we want to mess with the signal mask, and this is closer to our
intent anyway.

Now that we have select.cc.

It's going to manipulate process-global signal state, so multiple
instances do not make sense.

Closes #235.

Fixes #264.

Fixes #271 github issue.

Saves battery power.  Closes #243.

Simplifies access to private data, including the next commit.

git renders this diff poorly.  It's a bit better with --patience.

So that UI timeouts can adjust accordingly.

This prevents the client from waking up every 200 ms while the network is down.
Addresses #243.