Fix typo in comment.

src/backend/executor/execJunk.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/execJunk.c,v 1.44 2004/10/07 18:38:49 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/execJunk.c,v 1.45 2004/10/11 02:02:41 neilc Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -26,7 +26,7 @@
  * An attribute of a tuple living inside the executor, can be
  * either a normal attribute or a "junk" attribute. "junk" attributes
  * never make it out of the executor, i.e. they are never printed,
- * returned or stored in disk. Their only purpose in life is to
+ * returned or stored on disk. Their only purpose in life is to
  * store some information useful only to the executor, mainly the values
  * of some system attributes like "ctid" or rule locks.
  *