The attached patch fixes two issues with the powershell plugin:

• The build now fails when the script has parse errors, which it the current version doesn't do. (Because powershell.exe doesn't exits with 0 on parse errors.)
• It avoids ExecutionPolicy errors with the default ExecutionPolicy in place.

The changes do mean it depends om PowerShell v2, I assume (but didn't test) it will fail with PowerShell v1. But I doubt anyone considers this an issue.

I also made the plugin depend on Jenkins 1.450 because as is it didn't build with JDK 7.