SF patch 536615: travel cache

This is derived from the proposed patch and feedback to it.  This applies
the last-position cache behavior without an option, making the behavior
more like it is for interfaces with a mouse, where holding the mouse still
acts the same way as the travel cache.  The code is not #ifdef'd either.

src/options.c

@@ -516,6 +516,7 @@ initoptions()
 	for (i = 0; i < WARNCOUNT; i++)
 		warnsyms[i] = def_warnsyms[i].sym;
 	iflags.bouldersym = 0;
+	iflags.travelcc.x = iflags.travelcc.y = -1;
 	flags.warnlevel = 1;
 	flags.warntype = 0L;