FindCurses: Honor CURSES_NEED_NCURSES when curses is found

Take our CURSES_USE_NCURSES code path when CURSES_NEED_NCURSES is
enabled even if CURSES_CURSES_LIBRARY also happens to be found.

Applied-by: Rolf Eike Beer <eike@sf-mail.de>
FindCurses: Detect and satisfy ncurses dependency on tinfo

When ncurses is built with USE=tinfo we need to find "tinfo" as a
dependency of the main library.  Otherwise 'cbreak' is missing:

  ld: ...: undefined reference to symbol 'cbreak'
  ld: note: 'cbreak' is defined in DSO /lib/libtinfo.so.5 so try adding
            it to the linker command line

See https://bugs.gentoo.org/show_bug.cgi?id=468622 for more information.

Applied-by: Rolf Eike Beer <eike@sf-mail.de>
Merge topic 'ncurses-tinfo' into next

1f646c6c FindCurses: Detect and satisfy ncurses dependency on tinfo
0e4a2c7e FindCurses: Honor CURSES_NEED_NCURSES when curses is found