TxFileManager transactions for EVERYBODY!

- Everywhere I could find that does IO now does it through a transaction
  if possible. Most notably, the registry uses transactions.
- InstallList(), Install(), and Remove() all use transactions.
- CmdLine's Upgrade() is now a transaction around Install and Remove.
- Hand tested. OMG. It put back a botched upgrade as it was, including
  the registry.

Closes #181.