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/rollback.test

@@ -54,7 +54,7 @@ ifcapable conflict {
     catchsql {
       INSERT INTO t3 SELECT a FROM t1;
     }
-  } {1 {column a is not unique}}
+  } {1 {UNIQUE constraint failed: t3.a}}
   
   # Try to continue with the SELECT statement
   #