new bugs - implement 'whatis' of engravings

'/ e' (or '/ `') lists nearby engravings (including headstones) that
  the hero has read or felt (even if currently covered up) or can see
  on the map;
'/ E' (or '/ |') lists all such on the level.

If the hero remembers an engraving and then monsters scuff it out of
existence, it will magically disappear from the list of remembered
engravings when deleted.  I don't think that's worth bothering with.

[During testing, my pet seemed extremely reluctant to step on a
corridor engraving.  That could have been coincidence but it seemed
to keep happening until I moved so close that it had no choice.  I
wasn't carrying tripe.]

doc/fixes3-7-0.txt

@@ -2305,7 +2305,7 @@ make music improvisations more varied and interesting, as well as useful
 give a helpful tip when first entering "farlook" mode
 add a boolean option tips to disable all of the helpful tips
 add a tutorial level
-engravings appear on the map display
+engravings appear on the map display; 'whatis' can list them ('/e', '/E')
 option to create the character deaf
 add conduct for petless
 preceding #overview with the 'm' prefix brings up the overview display as a