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.

doc/fixes34.1

@@ -153,6 +153,8 @@ stone to flesh on a statue with contents would lose the contents if a
 	monster was on the same location as the statue
 steed movement would use your speed if walking step by step
 kicking a known, unseen monster would sometimes leave behind an extra I symbol
+applying a lance against a long worm could cause an impossible
+a knight applying a lance did not do a caitiff check
 
 
 Platform- and/or Interface-Specific Fixes