Mostly mechanical fixes and code clean ups:
- Add Group Policy to control per-user installs in Enterprise.
- Fix Omaha reports 100% install progress between download and install.
- Fix Wininet error comparison to HRESULT.
- Omaha client should not send install_data in Ping requests.
- Log secure status flag for WININET_E_DECODING_FAILED
- Remove gates that could potentially cause a deadlock.