Add a generation counter to the Schema object and enhance OP_VerifySchema

to also check the Schema generation.  Fix for
ticket [f7b4edece25c99].

FossilOrigin-Name: 36c04dd1695f0899b53ce58738181b146fc005ed

src/sqliteInt.h

@@ -671,6 +671,7 @@ struct Db {
 */
 struct Schema {
   int schema_cookie;   /* Database schema version number for this file */
+  int iGeneration;     /* Generation counter.  Incremented with each change */
   Hash tblHash;        /* All tables indexed by name */
   Hash idxHash;        /* All (named) indices indexed by name */
   Hash trigHash;       /* All triggers indexed by name */