optional_depends  "libpng"                 \
                  "--with-png=/usr/bin/"   \
                  "--without-png"          \
                  "for png output support" &&

optional_depends "readline"                                 \
		  "--with-readline=gnu --with-readline=/lib" \
                  "--with-readline"                          \
                  "use gnu readline instead of builtin readline"
