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/steal.c

@@ -492,7 +492,7 @@ steal(struct monst* mtmp, char* objnambuf)
 
 /* Returns 1 if otmp is free'd, 0 otherwise. */
 int
-mpickobj(register struct monst* mtmp, register struct obj* otmp)
+mpickobj(struct monst *mtmp, struct obj *otmp)
 {
     int freed_otmp;
     boolean snuff_otmp = FALSE;
@@ -706,7 +706,7 @@ mdrop_obj(
    even leaving the game entirely; when that happens, prevent them from
    taking the Amulet, invocation items, or quest artifact with them */
 void
-mdrop_special_objs(struct monst* mon)
+mdrop_special_objs(struct monst *mon)
 {
     struct obj *obj, *otmp;