This reverts commit 024d26ac0cd869826801889f1299df34676fdf57.

This was re-introducing Clang warnings since gboolean is signed.
I should have read the git blame before re-introducing gboolean...

* The previous solution was not wrong, but unnecessarily complex. We already have a flag
  for exactly this purpose.
* Avoid redundancies by introducing teco_machine_stringbuilding_set_codepage().

* It's contained in teco_machine_main_t which is created per macro call frame.
  So after macro calls, the machine no longer exists.
  It is therefore unsafe to undo its members indiscriminately.
* On the other hand, we must undo the codepage setting when run interactively,
  so it is now only undone when belonging to the commandline macro frame.
* This was actually causing memory corruptions on every fnkeys cursor movement, but never
  caused crashes - probably because the invalid pointers are always pointing to unused
  parts of the C call stack.
* Initially broken in b31b8871.

* this would also leak a few bytes on every of fnkeys.tes' movement commands

* Apparently, netbsd-curses overwrites the escdelay on initscr() (if $ESCDELAY is not set),
  so we have to apply the default 25ms after screen initialization.
* The info line is not drawn correctly on netbsd-curses, but only on st/simpleterm.
  I assume this is just a shortcoming of the included terminfo entry.

For instance, you can now write <23(1;)> without leaving anything on the stack.

* added TECO_ERROR_CLIPBOARD for all clipboard-related errors

* makes it possible, albeit cumbersome, to escape pattern match characters
* For instance, to search for ^Q, you now have to type
  S^Q^Q^Q^Q$.
  To search for ^E you have to type
  S^Q^Q^Q^E$.
  But the last character cannot be typed with carets currently (FIXME?).
  For pattern-only characters, two ^Q should be sufficient as in
  S^Q^Q^X$.
* Perhaps it would be more elegant to abolish the difference between string building
  and pattern matching characters to avoid double quoting.
  But then all string building constructs like ^EQq should operate at the pattern level
  as well (ie. match the contents of register q verbatim instead of being interpreted as a pattern).
  TECOC and TECO-64 don't do that either.
  If we leave everything as it is, at least a new string building construct should be added for
  auto-quoting patterns (analoguous to ^EN and ^E@).