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

src/vdbe.h

@@ -127,6 +127,12 @@ typedef struct VdbeOpList VdbeOpList;
 #define P4_KEYINFO_HANDOFF (-16)
 #define P4_KEYINFO_STATIC  (-17)
 
+/* Error message codes for OP_Halt */
+#define P5_ConstraintNotNull 1
+#define P5_ConstraintUnique  2
+#define P5_ConstraintCheck   3
+#define P5_ConstraintFK      4
+
 /*
 ** The Vdbe.aColName array contains 5n Mem structures, where n is the 
 ** number of columns of data returned by the statement.