* Also updated A_XXX attributes to WA_XXX, where the "new" wattr_set() APIs
  are used. This doesn't make a difference on ncurses and PDCurses, but the
  X/Open standard demands it.
* Allow color pairs up to 32767 instead of only up to 32766.
* We now always require Curses wide-character APIs due to Scinterm,
  which has to use mvwin_wch(). We were practically depending on wide-character
  support anyway, so this shouldn't really restrict portability.
* teco_curses_add_wc() has been simplified, now that we can rely on
  wide-char APIs. Perhaps it should be removed altogether?

* Unfortunately we cannot use `wbkgdset(win, A_REVERSE)` if we plan to
  use reverse text on this background, i.e. if we want to cancel out the background A_REVERSE.
* SciTECO therefore no longer uses background attributes, but only foreground attributes.
  When setting a reverse text, we XOR A_REVERSE into the previous attributes.
* This fixes control characters especially in the info line and popups, as well as rendering
  of the popup scroll bars.
* The command-line should now be rendered properly even on a dark-on-bright color theme
  (which does not yet exist).

This requires Unicode icon support to be enabled via ED.
The ellipsis symbol is shorter and more distinctive, allowing more of the original
text to be preserved before truncation.

* All non-ASCII characters are inserted as Unicode.
  On Curses, this also requires a properly set up locale.
* We still do not need any widechar Curses, as waddch() handles
  multibyte characters on ncurses.
  We will see whether there is any Curses variant that strictly requires
  wadd_wch().
  If this will be an exception, we might keep both widechar and non-widechar
  support.
* By convention gsize is used exclusively for byte sizes.
  Character offsets or lengths use int or long.

* Esp. with the new Scintilla version, the representation
  setting as part of every SCI_SETDOCPOINTER has turned out to
  be a performance bottleneck.
* The new Scintilla has a custom tweak/patch that disables any
  automatic representation setting in Scintilla itself.
  It is now sufficient to initialize the SciTECO-style representations
  only once in the lifetime of any view.