Bug 1269 - "backslash percent" not saved in effect presets

wxWidgets does special things with %.
It uses % to tell it of environment variables.

Rather than escaping %, it is simpler to disable the environment variables thing.

include/audacity/EffectAutomationParameters.h

@@ -73,6 +73,7 @@ public:
                    wxEmptyString,
                    0)
    {
+      SetExpandEnvVars(false);
       SetParameters(parms);
    }