* added some utility functions for working with ScriptDefaults

remove last_change from MultipleChoiceValue. It is now stored in the action, which makes more sense.

 * use ScriptValueP, wrapped in AnyValue, instead of the specialized value types
 * serialize these values using script syntax.
 * However: #ifdefed out for now, because I first wanted to commit the following change:

This requires a change to handling of last_change of MultipleChoiceValue. Instead of storing it in the field, it is now just part of the action. The action therefore has to be passed to Value::update.

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TODO: be consistent with thumbnail generation, where the value is converted to canonical form first.

Added ScriptDefault type, a wrapper that indicates that a value is in the default state. This will replace Defaultable<>

formating; explicitly return nil from text_to_color on failure. The latter is needed because a warning will be added to 2.0.1 about missing returns (not yet in trunk)

use correct border style instead of always using wxBORDER_THEME. This issue is fixed in wxMSW 2.9, but we are not ready for that yet.

This means that we no longer need to pass smart pointers to this in thisP arguments, since we can construct a new intrusive_ptr to the same object from a regular C++ pointer.

(This change is manually merged from the non_null_pointer branch)

This means that we are more explicit about type conversions.

allow opening set files in directories from File->Open dialog: they were returned as "x.mse-set\set.mse-set". Strip the last part.