Miscellanous fixes to merge

These are the commits from the "miscellanous-fixes" branch that are okay to merge in.

Bugs fixed include the following:

• CTF flags respawning incorrectly: they cannot z position themselves correctly, and they cannot flip themselves.
• The weird "jumping" spring/monitor effect: this is the result of an internal mobj_t pointer (tmfloorthing, specifically) not resetting itself to NULL for the next object's thinker, resulting in Z movement code thrusting the object vertically at tmfloorthing->momz.

src/p_local.h

@@ -276,7 +276,7 @@ boolean P_LookForPlayers(mobj_t *actor, boolean allaround, boolean tracer, fixed
extern boolean floatok;
extern fixed_t tmfloorz;
extern fixed_t tmceilingz;
-extern mobj_t *tmfloorthing, *tmthing;
+extern mobj_t *tmfloorthing, *tmhitthing, *tmthing;
extern camera_t *mapcampointer;
/* cphipps 2004/08/30 */