NEW: Added support for thread static object tracking
NEW: Extended Variant structure to support reading/writing file-times as DateTime objects, and writing string objects.
WIC MetadataQueryWriter now also uses the Variant structure, just like the MetadataQueryReader. Some types - like DateTime - are marshaled differently by Marshal.GetNativeVariantForObject. See http://archive.msdn.microsoft.com/wictools for details (we should actually mimic all the code in it)
Added TryGetMetadataByName method to the WIC MetadataQueryReader. This method doesn't throw an exception when the requested property is not found or not supported; instead null is returned.

Added QueryPaths property to the WIC MetadataQueryReader. This returns all the query paths.
FIX: The ColorContexts property of the BitmapDecoder and BitmapFrameDecode never worked; WIC requires the color contexts objects to be created before calling the method (very odd indeed). Marked this property as obsolete. Replaced it by a TryGetColorContexts method. This method doesn't throw an exception when requesting the color contexts of a bitmap that does not support color contexts; instead it returns null.