found_artifact() groundwork

Lay groundwork for generating a log event when finding an artifact
on the floor or carried by a monster.  This part should not produce
any change in behavior.

Move g.artidisco[] and g.artiexist[] out of the instance_globals
struct back to local within artifact.c.  They are both initialized
at the start of a game (and only used in that file) so don't need
to be part of any bulk reinitialization if restart-instead-of-exit
ever gets implemented.

Convert artiexist[] from an array of booleans to an array of structs
containing a pair of bitfields.  artiexist[].exists is a direct
replacement for the boolean; artiexist[].found is new but not put to
any significant use yet.  If will be used to suppress the future
found-an-artifact event for cases where a more specific event (like
crowning or divine gift as #offer reward) is already produced.

Remove g.via_naming altogether and add an extra argument to oname()
calls to replace it.

Add an extra argument to artifact_exists() calls.

src/objnam.c

@@ -4787,7 +4787,7 @@ readobjnam(char *bp, struct obj *no_wish)
                 d.name = novelname;
         }
 
-        d.otmp = oname(d.otmp, d.name);
+        d.otmp = oname(d.otmp, d.name, ONAME_NO_FLAGS);
         /* name==aname => wished for artifact (otmp->oartifact => got it) */
         if (d.otmp->oartifact || d.name == aname) {
             d.otmp->quan = 1L;
@@ -4799,7 +4799,7 @@ readobjnam(char *bp, struct obj *no_wish)
     /* and make them pay; charge them for the wish anyway! */
     if ((is_quest_artifact(d.otmp)
          || (d.otmp->oartifact && rn2(nartifact_exist()) > 1)) && !wizard) {
-        artifact_exists(d.otmp, safe_oname(d.otmp), FALSE);
+        artifact_exists(d.otmp, safe_oname(d.otmp), FALSE, FALSE);
         obfree(d.otmp, (struct obj *) 0);
         d.otmp = (struct obj *) &cg.zeroobj;
         pline("For a moment, you feel %s in your %s, but it disappears!",