Issue 482 Support executable copy instructions for image objects

[fsteimke]

Although copying of media objects is "not our problem" we should help the users of the stylesheets.

A precondition is that we know the filepath of the generated HTML file(s). This is the case when we do chunking ($cunk-output-base-uri).

I suggest to introduce a new attribute ghost:sourcefile for html elements for mediaobjects. I did it only for images, because i don't know if you like this approach.

With this new attribute, we can

• generate executable copy instructions and execute them in the stylesheets. This is maximum support, but needs a function file:copy. Needs Saxon PE or EE Edition or a alternative implementation of expath:file. Works for users of Oxygen (Saxon EE included).
• generate an external file with copy instructions (maybe a shell script). Not included in this PR, because result-document conflicted with XSpec.

Greetings, Frank

[fsteimke]

Withdrawn: an improved solution will be provided soon. Frank Steimke