Make sure that all accounts are saved before the end of the transaction

[jwasinger]

Fixes #225 .

[holgerd77]

Is this ready for review?

[cdetrio]

Can we create a test case for this before merging the fix?

[jwasinger]

This is a weird one. I tried to create a test case to cover this but it didn't fail when run through ethereumjs-vm.

My best guess is that, when this scenario occurs in remix/testrpc, the state trie cache is not being flushed properly at the end of the txn, and the account is deleted.

But when run as a state test, somehow this is not the case.

[axic]

A few lines above this code is broken:

   this.cache.getOrLoad(address, function (err, account) {
     cb(err, account.exists)
   })

If err is true then account should be null or undefined and this code would dereference it.