added whatif package

_scripts/whatif.ps1

@@ -0,0 +1,40 @@
+<#
+This script implements WhatIf functionality. When you use it, it will 
+    - backup a package prior a call to update
+    - save updater output to another folder
+    - restore an original package after update finishes
+
+Use it by adding a switch parameter to update.ps1 and surrounding update
+by backup and restore functions:
+
+    param( [switch]$WhatIf )
+
+    ...
+    
+    backup 
+    update ...
+    restore
+
+#>
+
+function backup()  { 
+    if (!$WhatIf) { return }
+    Write-Warning "WhatIf passed - package files will not be changed"
+
+    $packageName = Split-Path -Leaf $MyInvocation.PSScriptRoot
+    $d = "$Env:TEMP\au\$packageName"
+
+    rm $d\* -Recurse -ea 0
+    cp . $d\_backup -Recurse 
+}
+
+function restore() { 
+    $packageName = Split-Path -Leaf $MyInvocation.PSScriptRoot
+    $d = "$Env:TEMP\au\$packageName"
+
+    cp . $d\_output -Recurse 
+    rm .\* -Recurse
+    cp $d\_backup\* . -Recurse 
+
+    Write-Warning "Package saved to: $d\_output"
+}