scrolls written while blind; scrolls of mail

Make a fix suggested during beta testing:  you can read scrolls while
blind if you know the label, and you can write a scroll with a magic
marker while blind, but the result was flagged as description unknown
so you couldn't read the newly written scroll until regaining sight
or obtaining object identification.  So change writing a previously
discovered scroll while blind to set dknown since a successful write
always yields the type of scroll requested.  Getting lucky while
attempting to write an undiscovered scroll--which has to be done by
scroll's type name (for instance "food detection") rather than by its
label ("YUM YUM")--still leaves the description flagged as unknown
since hero hasn't seen the what sort of label the new scroll has.

Along the way I got side-tracked by the possibilty of writing a scroll
of mail.  It's allowed and yielded the same result as finding such a
scroll in bones, or wishing for one:  when read, it was junk mail from
Larn.  Make one written via marker give different feedback since it
comes from creation of a stamped scroll without any stamps available.

Also, suppress an "argument not used" warning for readmail().

doc/fixes36.1

@@ -32,6 +32,8 @@ falling asleep when reading dull spellbook ignored sleep resistance
 getpos() complaint about invalid movement keystroke didn't describe meta-chars
 	accurately
 'realtime' value in xlogfile was incorrect if 'checkpoint' option was active
+make a previously-discovered scroll written with marker while blind have its
+	label known so it can be read while blind
 
 
 Platform- and/or Interface-Specific Fixes
@@ -51,6 +53,7 @@ X11: core bug for '`' (backtick) command was only noticed by X11 interface,
 General New Features
 --------------------
 naming Sting or Orcrist now breaks illiterate conduct
+different feedback for reading a scroll of mail created by writing with marker
 
 
 Platform- and/or Interface-Specific New Features