Windows: Modify afscreds.exe and afs_config.exe to be UAC compatible

Windows: Modify afscreds.exe and afs_config.exe to be UAC compatible

afscreds.exe:
 1. disable the drive mapping and advanced tabs.
 2. on exit, remove the option to stop the service.

afs_config.exe:
 1. disable the drive mapping tab

Removing this functionality by default will address some of the
problems while permitting users that wish to continue using these tools
to do so.   The drive mapping tab can be re-enabled setting the registry
value to be non-zero:

  {HKCU,HKLM}\Software\OpenAFS\Client DWORD "ShowMountTab"

LICENSE MIT

Reviewed-on: http://gerrit.openafs.org/663
Tested-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>