* The GTK version logs additional warnings, so we cannot
  match verbatim against stderr.
  Instead we only look for a line beginning with `Warning:` or `Error:`.
* We now also test info messages (`1^A`).

* I.e. you can now log warnings and errors from SciTECO code as well.
* We do not need a version of ^A accepting code points, since this is
  supported by ^T already.

In TECO-11 pattern matching constructs do not allow backtracking,
while the PCREs currently generated do allow backtracking.
This would be easy to fix, but there should also be constructs
to re-enable the backtracking semantics.
I left only a Known Bug test case for the time being.

* teco_string_diff() could return a number of bytes in the middle of
  an Unicode sequence. It now also requires Unicode strings.
* Added a missing Unicode-validity check when replacing command lines (`{` and `}`).
  teco_cmdline_insert() should really be refactored, though (FIXME).
* Added test case

* Turns out that it works perfectly with the default --enable-malloc-replacement
  as malloc() is replaced globally.
* Added note to configure.ac that malloc() replacement may be useful on platforms
  without a global symbol namespace - you just have to link statically (--enable-static-executables)
  as well.
  This wasn't necessary on Haiku, though.
* Only the test suite required a minor fix since Haiku doesn't support `ulimit`.
* The Gtk interface is broken though on Haiku: You cannot type dead keys,
  Ctrl and AltGr combinations.
  Doesn't appear to be SciTECO-specific though. The libraries simply doesn't
  report modifiers. Appears to be a bug in Haiku's GTK 3 port,
  at least in their Beta5 branch. It can be reproduced with gtk-demo as well.
* This opens the door for contributing a port into HaikuPorts.
  This will probably be Curses-only for the time being (see above).

It causes build failures on OBS for several Linux distributions.
It generally works on Linux, so it's probably related to Xvfb.

Hopefully fixes the OBS build errors.

This is useful to launch from a terminal without "blocking" this terminal.
There are tools like nohup and daemonize (BSD) to do the same, but having it
builtin is shorter to write.