Standardize the error messages generated by constraint failures to a format

of "$TYPE constraint failed: $DETAIL".  This involves many changes to the
expected output of test cases.

FossilOrigin-Name: 54b221929744b1bcdbcc2030fef2e510618afd41

test/table.test

@@ -464,7 +464,7 @@ do_test table-10.1 {
     CREATE TABLE t6(a REFERENCES t4(a) NOT NULL);
     INSERT INTO t6 VALUES(NULL);
   }
-} {1 {t6.a may not be NULL}}
+} {1 {NOT NULL constraint failed: t6.a}}
 do_test table-10.2 {
   catchsql {
     DROP TABLE t6;