fix #H8579 - mimics mimicking shop objects

Showing the price of a shop object when examining it with '/' or ';'
didn't include a price if it was actually a mimic.  This makes fake
objects have prices when appropriate, but it is only a partial fix
because moving away from a mimic causes nethack to forget the fake
object's dknown flag for most types of objects.

That could be solved by adding an mobj field to mon->mextra, which
will break save compatibility, or by adding a whole extra set of
object glyphs for object-with-dknown-set.  The latter could probably
be done without breaking backwards save compatibility (new program
using old files) but it seems like more effort that it'd be worth and
it would break forwards save compatibility (old program attempting to
use new files--something we've never claimed to support).

doc/fixes36.2

@@ -1,4 +1,4 @@
-$NHDT-Branch: NetHack-3.6.2-beta01 $:$NHDT-Revision: 1.304 $ $NHDT-Date: 1555552900 2019/04/18 02:01:40 $
+$NHDT-Branch: NetHack-3.6.2-beta01 $:$NHDT-Revision: 1.305 $ $NHDT-Date: 1555627306 2019/04/18 22:41:46 $
 
 This fixes36.2 file is here to capture information about updates in the 3.6.x
 lineage following the release of 3.6.1 in April 2018. Please note, however,
@@ -484,6 +484,7 @@ using 'O' to set status hilites for any status condition (Blind, &c) and
 	retain one of the chosen attributes
 when u.uhp==-1 became a flag to suppress status updating, if game ended when
 	hero died with exactly -1 HP, status would be blank during disclosure
+mimic mimicking a shop item didn't show any shop price for whatis and glance
 tty: turn off an optimization that is the suspected cause of Windows reported
 	partial status lines following level changes
 tty: ensure that current status fields are always copied to prior status