refine #1106 - invent action: item lookup

Only show the '/' menu choice for context-sensitive inventory item
action if data.base look up for the item will find something.  Lack
of '/' is as informative as "you don't know anything about that".

Harder to implement than expected but seems to be working ok.

This also changes the menu for the '/' command, replacing cryptic /^
and /" with /t and /T so that listing near traps or all traps is more
like listing near|all objects|monsters.  I put caret and double-quote
in as group accelerators; double-quote works on tty, caret gets
intercepted as "menu first page" so doesn't.  I didn't check other
interfaces since supporting that doesn't seem to be worth the bother.

Also a little bit of reformatting.

include/extern.h

@@ -2098,6 +2098,7 @@ extern char *monhealthdescr(struct monst *mon, boolean, char *);
 extern void mhidden_description(struct monst *, boolean, char *);
 extern boolean object_from_map(int, coordxy, coordxy, struct obj **);
 extern const char *waterbody_name(coordxy, coordxy);
+extern boolean ia_checkfile(struct obj *);
 extern int do_screen_description(coord, boolean, int, char *, const char **,
                                  struct permonst **);
 extern int do_look(int, coord *);