CA-106455: XenCenter Installation: multiple install on same OS when selected installation for all users; Asking for .NET 3.5 while repair or uninstall.

Changed the way we check whether .NET 2.0/.NET 3.5 framework is already
installed on the user machine or not.

Signed-off-by: Adrian Jachacy <Adrian.Jachacy@citrix.com>
CA-106455: XenCenter Installation: multiple install on same OS when selected installation for all users; Asking for .NET 3.5 while repair or uninstall.

1. Added missing copyright header to XenCenter.l10n.diff file.
2. Added -ext WiXNetFxExtension to CANDLE command in xenadmin-build.sh
file.

Signed-off-by: Adrian Jachacy <Adrian.Jachacy@citrix.com>