ncurses 6.0 - patch 20171223

ncurses 6.0 - patch 20171223

+ modify ncurses-examples to quiet const-warnings when building with
  PDCurses.
+ modify toe to not exit if unable to read a terminal description,
  e.g., if there is a permission problem.
+ minor fix for progs/toe.c, using _nc_free_termtype2.
+ assign 0 to pointer in _nc_tgetent_leak() after freeing it. Also
  avoid reusing pointer from previous successful call to tgetent
  if the latest call is unsuccessful (patch by Michael Schroeder,
  OpenSuSE #1070450).
+ minor fix for test/tracemunch, initialize $awaiting variable.