[sldev] OpenJPEG decoder update

[Tofu Linden]

David Fries wrote:
> The viewer code has a notable lack of comments.  Here is a patch to
> help that out a little bit.  It also destroys the cio and dinfo
> structures before checking if an image was returned in getMetadata().
> That way they aren't destroyed in two different places. 

Thanks, I'll combine these with the other patch for the QA pass.
Comments are always good.  I haven't applied the llimagej2coj.h
change since you also document this interface in the parent class
definition which hopefully people know to defer to, to save keeping
two identical interface docs in sync.

Ta,
- Tofu