fix odd messages caused by buffer re-use

Reported and diagnosed by entrez:
"The <mon> yanks <two-handed weapon> from your corpses!"

It became unwielded and that triggered a perm_invent update and
such updates reformat entire inventory, so if that contains a dozen
or more items it will use all the obuf[] static buffers as least
once.  In this case, the bullwhip code had plural of "hand" in one
of those buffers and by the time it delivered the message which
used that, the value had been clobbered.

As the diagnosis mentioned, it can be tricky to reproduce since
either &obuf[0] or &obuf[PREFIX] might be used and if the value
being clobbered didn't overlap, the effect wasn't noticeable.

Instead of fixing the bullwhip message, this changes inventory
display so that it should no longer churn through all the buffers.

It also adds a fixes entry for #K3401, which was already fixed for
3.7 but I hadn't been able to reproduce it for 3.6.x (which I now
blame on the PREFIX trickiness).

include/extern.h

@@ -1762,6 +1762,7 @@ extern void objects_globals_init(void);
 
 /* ### objnam.c ### */
 
+extern void maybereleaseobuf(char *);
 extern char *obj_typename(int);
 extern char *simple_typename(int);
 extern char *safe_typename(int);