CMS Package, data installer, using allowOverwrite fail for data not already existing

[mawtex]

The allowOverwrite attribute which you can set on elements for DataPackageFragmentInstaller will cause an exception, if data being loaded is new (does not exist in the system already).

Repro:

1. Install attached Orckestra.Test.BeforeOverwriteData.zip as local package
2. Install attached Orckestra.Test.OverwriteData.zip as local package

Expected:
In step 1, we install 3 data elements (Item 1, Item 3, Item 4).
In step 2, we update "Item 3" and add new data element "Item 2"

Actual:
Package install fail in step 2 with "Non-static method requires a target" error text.

Orckestra.Test.BeforeOverwriteData.zip
Orckestra.Test.OverwriteData.zip

Sample use of the allowOverwrite attribute:

<mi:PackageFragmentInstallers>
	<mi:Add installerType="Composite.Core.PackageSystem.PackageFragmentInstallers.DataPackageFragmentInstaller, Composite" uninstallerType="Composite.Core.PackageSystem.PackageFragmentInstallers.DataPackageFragmentUninstaller, Composite">
		<Types>
			<Type type="Orckestra.Test.Data" allowOverwrite="true">
				<Data dataScopeIdentifier="public" dataFilename="~\Datas\Orckestra.Test.Datas_public.xml" />
			</Type>
		</Types>
	</mi:Add>
</mi:PackageFragmentInstallers>

[wwwysocki]

Verified in 20161109.3 (fix-bugs)