ncurses 6.0 - patch 20170212

ncurses 6.0 - patch 20170212

+ build-fixes for PGI compilers (report by Adam J. Stewart)
  + accept whitespace in sed expression for generating expanded.c
  + modify configure check that g++ compiler warnings are not used.
  + add configure check for -fPIC option needed for shared libraries.
+ let configure --disable-ext-funcs override the default for the
  --enable-sp-funcs option.
+ mark some structs in form/menu/panel libraries as potentially opaque
  without modifying API/ABI.
+ add configure option --enable-opaque-curses for ncurses library and
  similar options for the other libraries.