[Bf-python] Image attributes

[Ken Hughes]

A quick heads-up after looking into this:

Ed Blake wrote:
> In 2.43 image handling was changed.  Yesterday I needed to update a import
> script that worked with image texture attributes that no longer exist.  The
> problem is their functionality hasn't been replaced by anything in the image
> module!
> 
> Here are a few things that are missing:
> There is no way to set image type - movie and internal are set automatically,
> but how do you tell Blender your image is part of a sequence?

Simple to fix: added an image.source attribute

> No way to set movie/sequence length, and image.end is broken - currently
> image.start/image.end only take values between 1 and 127?  Was this ever a
> real limitation in Blender?
> No access to the (new) Auto-Update feature.

Not so simple: the Image refactor Ton did prior to 2.43 makes these 
attribute not of the image but of the context; texture, node, etc. 
Makes sense, but means you will have to access them through those 
classes: Texture.imagestart, etc.  When a Nodes API is written (if it 
is), it would access the same attributes in that context.

Ken