fix audit issues

Author: nathanielCherian

examples/next.cash

@@ -3,6 +3,7 @@ pragma cashscript ^0.7.0;
 contract P2PKH() {
     function spend() {
         bytes2 left, bytes2 right = 0x123456.split(2);
+        int constant c = 5;
         require(left == right);
         require(c*2 == 2);
         require(tx.outputs[0].value == tx.inputs[this.activeInputIndex].value - 10*10);