R919 - applying lances

Fixes 2 bugs:
1) an impossible() could occur if you applied a lance against a long worm
because the code uses thitmonst to do the hitting, but didn't set bhitpos,
which is required before calling thitmonst.
Add the missing assignment.
2) applying a lance would never mark a knight as a caitiff.  Added a new
check_caitiff function and called it from the 2 existing checks and in
the lance code.

src/apply.c

@@ -2367,6 +2367,8 @@ use_pole (obj)
 	if ((mtmp = m_at(cc.x, cc.y)) != (struct monst *)0) {
 	    int oldhp = mtmp->mhp;
 
+	    bhitpos = cc;
+	    check_caitiff(mtmp);
 	    (void) thitmonst(mtmp, uwep);
 	    /* check the monster's HP because thitmonst() doesn't return
 	     * an indication of whether it hit.  Not perfect (what if it's a