More threading updates

[Jonathan Blandford <jrb redhat com>]

Hey,

So I fixed a lot of the missing/broken features in the threading branch.
Rendering, page changing, saving, printing and indexing all work now.
Indexing is on the slow side[1], but we know how to speed that up by a
lot in poppler.  That leaves four major features left to be done:

 * links in the page.  I have links half working on my machine.  It
   needs a few poppler changes, so I'm holding off on committing them,
   but once that change is made, we should be fine.

 * Porting the gv backend over.  I know Marco gave a quick look at this,
   and we ran into some nastiness.  This turned out to not be as simple
   as I'd hoped.

 * reenabling find.  This will be tricky to write, and I think I'd
   rather wait until we get the glib bindings before attempting it.  I
   can certainly attempt it, though.  It is going to change the locking
   a bit.

 * Text selection.  Similar technical constraints to the find issue,
   though as before, I still don't like the rectangular selection.  I'd
   much rather have a hand to move the page around with first.

I really don't want to move over to poppler-glib until the threading
branch is merged to head, and I feel like I've been holding up new
feature work to have such a large change on a branch.  Things like
smooth-scrolling and continuous views shouldn't be done until we merge
back.

When should I think about merging back the branch so that we can start
doing new feature work again?  Would people find it acceptable to do the
merge even with all the above broken?  Or should I keep moving forward
with fixing the features?

Thanks,
-Jonathan

[1] 45 seconds w/o updated images with the PDF reference.