[packages] rtorrent: fix compile

ncurses was not detected on some build systems
Error:
configure: WARNING: could not find a working ncursesw/curses.h, ncursesw.h or ncurses.h

some unknown symbols were discovered when linking libtorrent
usr/lib/libtorrent.so: undefined reference to `gzopen64'
usr/lib/libtorrent.so: undefined reference to `gzclose'
usr/lib/libtorrent.so: undefined reference to `gzwrite'

Signed-off-by: Dirk Neukirchen <dirkneukirchen@web.de>