Further tweak wording of error messages about bad CONTINUE/EXIT statements.

Per discussion, a little more verbosity seems called for.

src/pl/plpgsql/src/pl_gram.y

@@ -1676,7 +1676,8 @@ stmt_exit		: exit_type opt_label opt_exitcond
 							if (label == NULL)
 								ereport(ERROR,
 										(errcode(ERRCODE_SYNTAX_ERROR),
-										 errmsg("there is no label \"%s\" surrounding this statement",
+										 errmsg("there is no label \"%s\" "
+												"attached to any block or loop enclosing this statement",
 												$2),
 										 parser_errposition(@2)));
 							/* CONTINUE only allows loop labels */

src/test/regress/expected/plpgsql.out

@@ -2864,7 +2864,7 @@ begin
     end;
 end;
 $$ language plpgsql;
-ERROR:  there is no label "no_such_label" surrounding this statement
+ERROR:  there is no label "no_such_label" attached to any block or loop enclosing this statement
 LINE 5:             continue no_such_label;
                              ^
 -- should fail: no such label
@@ -2877,7 +2877,7 @@ begin
     end;
 end;
 $$ language plpgsql;
-ERROR:  there is no label "no_such_label" surrounding this statement
+ERROR:  there is no label "no_such_label" attached to any block or loop enclosing this statement
 LINE 5:             exit no_such_label;
                          ^
 -- should fail: CONTINUE can't reference the label of a named block