Save file fails with some [var] contents

[bgribble]

Saving a [var] attempts to serialize the current contents to JSON. Some values can't be serialized without help.

Alternatives:

• Don't save the value. Saving it is usually a distraction, since the state of the patch can be surprisingly different from what you expect
• Extend the serializer to work better for unserializable types
• Attempt to save, catch exceptions, don't error out if a value can't be serialized.