Added failing test

Repro for pester#353 in PowerShell 2.0.  I wasn't able to reproduce this using a function for some reason, but mocking Start-Process does cause the error to occur.

Incidentally, it's being caused by this line in MockPrototype:

[object] $ArgumentList = Get-Variable -Name args -ValueOnly -Scope Local -ErrorAction $IgnoreErrorPreference

It appears to be a problem when the mocked command also has an -ArgumentList parameter, which contains Validation attributes such as ValidateNotNullOrEmpty() (though why I wasn't able to reproduce this with a mocked function instead of Start-Process, I don't know.)

Functions/Mock.Tests.ps1

@@ -1292,3 +1292,15 @@ Describe 'Mocking commands with potentially ambigious parameter sets' {
         Assert-MockCalled SomeFunction -ParameterFilter { $p1 -eq 'Whatever' }
     }
 }
+
+Describe 'When mocking a command that has an ArgumentList parameter with validation' {
+    Mock Start-Process { return 'mocked' }
+
+    It 'Calls the mock properly' {
+        $hash = @{ Result = $null }
+        $scriptBlock = { $hash.Result = Start-Process -FilePath cmd.exe -ArgumentList '/c dir c:\' }
+
+        $scriptBlock | Should Not Throw
+        $hash.Result | Should Be 'mocked'
+    }
+}