(chocolatey#89) Remove cpack shims on package upgrades

This commit updates the installation/upgrading of
the package to remove the cpack shim if they are
signed with the expected authenticode signature
thumbprint.

The thumbprint being checked against in the thumbprint
used in Chocolatey v0.12.1.

The code added makes it easy to extend it when needed
for removal of other shims as well.

nuget/chocolatey/tools/chocolateysetup.psm1

@@ -30,6 +30,41 @@ param (
   }
 }
 
+function Remove-ShimWithAuthenticodeSignature {
+  param (
+    [string] $filePath
+  )
+  if (!(Test-Path $filePath)) {
+    return
+  }
+
+    $signature = Get-AuthenticodeSignature $filePath -ErrorAction SilentlyContinue
+
+    if (!$signature -or !$signature.SignerCertificate) {
+      Write-ChocolateyWarning "Shim found in $filePath, but was not signed. Ignoring removal..."
+      return
+    }
+
+    $possibleSignatures = @(
+      'RealDimensions Software, LLC'
+      'Chocolatey Software, Inc\.'
+    )
+
+    $possibleSignatures | % {
+      if ($signature.SignerCertificate.Subject -match $_) {
+        Write-Output "Removing shim $filePath"
+
+        if (Test-Path "$filePath.ignore") {
+          Remove-Item "$filePath.ignore"
+        }
+      }
+    }
+
+    if (Test-Path $filePath) {
+      Write-ChocolateyWarning "Shim found in $filePath, but did not match any known signatures. Ignoring shim removal..."
+    }
+}
+
 function Initialize-Chocolatey {
 <#
   .DESCRIPTION
@@ -331,6 +366,17 @@ param(
           }
         }
       }
+
+      $shimsToRemove = @("cpack.exe")
+      Get-ChildItem -Path $to -Recurse -Include $shimsToRemove |
+        % {
+          try {
+            Remove-ShimWithAuthenticodeSignature -filePath $_
+          }
+          catch {
+            Write-ChocolateyWarning "Unable to remove `'$_`'. Please remove the file manually."
+          }
+        }
   }
 }