Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Simply let teken_stress use arc4random.

This makes it run quite a bit faster, since it makes system calls less
often.

Add proper build infrastructure for teken.

I'm not sure whether we should install teken as a library on any stock
FreeBSD installation, but I can imagine people want to tinker around
with it now and then. Create a /sys/teken/libteken, which holds a
Makefile to install a shared library version of the terminal emulator,
complete with a manpage.

Also add Makefiles for the demo/stress applications, to build it against
the shared library.

Make the fuzzer a bit more useful by forcing 7-bit data into it.

Getting valid UTF-8 sequences is quite unlikely, so we'd better just
convert data to 7 bits and make it extra likely for escape sequences to
occur.

Move libteken out of the syscons directory.

I initially committed libteken to sys/dev/syscons/teken, but now that
I'm working on a console driver myself, I noticed this was not a good
decision. Move it to sys/teken to make it easier for other drivers to
use a terminal emulator.

Also list teken.c in sys/conf/files, instead of listing it in all the
files.arch files separately.

Make the demo/stress tools build again, after my changes to param().

Replace syscons terminal renderer by a new renderer that uses libteken.

Some time ago I started working on a library called libteken, which is
terminal emulator. It does not buffer any screen contents, but only
keeps terminal state, such as cursor position, attributes, etc. It
should implement all escape sequences that are implemented by the
cons25 terminal emulator, but also a fair amount of sequences that are
present in VT100 and xterm.

A lot of random notes, which could be of interest to users/developers:

- Even though I'm leaving the terminal type set to `cons25', users can
do experiments with placing `xterm-color' in /etc/ttys. Because we
only implement a subset of features of xterm, this may cause
artifacts. We should consider extending libteken, because in my
opinion xterm is the way to go. Some missing features:

- Keypad application mode (DECKPAM)
- Character sets (SCS)

- libteken is filled with a fair amount of assertions, but unfortunately
we cannot go into the debugger anymore if we fail them. I've done
development of this library almost entirely in userspace. In
sys/dev/syscons/teken there are two applications that can be helpful
when debugging the code:

- teken_demo: a terminal emulator that can be started from a regular
xterm that emulates a terminal using libteken. This application can
be very useful to debug any rendering issues.

- teken_stress: a stress testing application that emulates random
terminal output. libteken has literally survived multiple terabytes
of random input.

- libteken also includes support for UTF-8, but unfortunately our input
layer and font renderer don't support this. If users want to
experiment with UTF-8 support, they can enable `TEKEN_UTF8' in
teken.h. If you recompile your kernel or the teken_demo application,
you can hold some nice experiments.

- I've left PC98 the way it is right now. The PC98 platform has a custom
syscons renderer, which supports some form of localised input. Maybe
we should port PC98 to libteken by the time syscons supports UTF-8?

- I've removed the `dumb' terminal emulator. It has been broken for
years. It hasn't survived the `struct proc' -> `struct thread'
conversion.

- To prevent confusion among people that want to hack on libteken:
unlike syscons, the state machines that parse the escape sequences are
machine generated. This means that if you want to add new escape
sequences, you have to add an entry to the `sequences' file. This will
cause new entries to be added to `teken_state.h'.

- Any rendering artifacts that didn't occur prior to this commit are by
accident. They should be reported to me, so I can fix them.

Discussed on: current@, hackers@
Discussed with: philip (at 25C3)