Clean up error messages associated with rules and views.

Fix parser error message when an operator is not found
 to not explicitly claim that there is more than one.

Author: Thomas G. Lockhart

src/test/regress/expected/errors.out

@@ -139,7 +139,7 @@ ERROR:  parser: parse error at or near ";"
 QUERY: drop rule 314159;
 ERROR:  parser: parse error at or near "314159"
 QUERY: drop rule nonesuch;
-ERROR:  RewriteGetRuleEventRel: rule "nonesuch" not found
+ERROR:  Rule or view 'nonesuch' not found
 QUERY: drop tuple rule nonesuch;
 ERROR:  parser: parse error at or near "tuple"
 QUERY: drop instance rule nonesuch;

src/test/regress/expected/geometry.out

@@ -87,7 +87,7 @@ one|f1
 
 QUERY: SELECT '' AS count, p.f1, l.s, l.s # p.f1 AS intersection
    FROM LSEG_TBL l, POINT_TBL p;
-ERROR:  There is more than one possible operator '#' for types 'lseg' and 'point'
+ERROR:  Unable to identify an operator '#' for types 'lseg' and 'point'
 	You will have to retype this query using an explicit cast
 QUERY: SELECT '' AS thirty, p.f1, l.s, p.f1 ## l.s AS closest
    FROM LSEG_TBL l, POINT_TBL p;