Fix some incorrect comments and typos in comments. Add testcase() macros

to some of the new record comparison code.

FossilOrigin-Name: b83cfe899d84fe9d61540e9984321ca30401638c

src/btree.c

@@ -4576,7 +4576,7 @@ int sqlite3BtreeMovetoUnpacked(
          || pIdxKey->default_rc==-1
     );
   }else{
-    xRecordCompare = 0; /* Not actually used.  Avoids a compiler warning. */
+    xRecordCompare = 0; /* All keys are integers */
   }
 
   rc = moveToRoot(pCur);