Between calls to `^T`, the original key-press-event handler might
enqueue events, that we must first process and report with `^T`.
Otherwise it would be easy to provoke apparent double-reporting of keys after
input loops like `<^T:;>`.

* There was a logic error in teco_interface_getch() that caused Curses function key
  codes to be returned directly. These codes however are useless to macro authors and
  can be confused with codepoints. You cannot report function keys in the same "namespace"
  along with Unicode codepoints.
  They are now filtered out.
* Also make sure that Backspace and Return are reported as 8 and 10 respectively
  in all Curses variants.
  All control codes reported by Curses are passed down unmodified - in contrast to
  the command-line input handling. I.e. 13 is not normalized to 10.
* PDCursesMod/WinGUI may return bogus key presses, that also have to be filtered out
  as we already did in the main input handling.
  A function teco_interface_check_key() has been introduced.
* NOTE: teco_interface_blocking_getch() already makes sure that recovery files are dumped
  even when blocking in `^T`.

* This is a gimmick pseudo-game for driving a tank around your buffer.
* The tank is "animated" and crushes non-space characters it drives over.
* When shooting, it deletes characters that get hit.
* When escaping, the tank explodes and leaves a "crater" behind.

There is no way to catch errors in ^Q since :^Q is already taken
as a dot-to-line conversion. :^Q is an extension, so we might still
want to repurpose it.

There has been a regression affecting early uses of `.device`.
See https://savannah.gnu.org/bugs/?67992

When editing TECO source files with fnkeys.tes, you could get unexpected cursor jumps
since SCI_GETCOLUMN counts all control characters as single columns and would always expand
tabs, even if tabs are drawn like control codes.

This could have been changed in Scintilla itself, but Neil decided that
SCI_GETCOLUMN and SCI_FINDCOLUMN will not be changed.
See https://groups.google.com/g/scintilla-interest/c/aqxapyAcRiA

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.

5 minutes was probably a bit too conservative.

Will rarely be of use in SciTECO, but it's part of the officially merged commit.