Add unit test for rendering image tag with a missing image
add failing test for #801
Define a custom exception type for IO errors thrown when opening source images, and catch that in InageNode.render so that we're not masking unrelated IOErrors elsewhere in the get_rendition process
catch SourceImageIOError when rendering image formats - fixes #801
Fix 'TypeError at /admin/pages/ID/edit/preview/ serve_subpage() takes exactly 2 arguments (1 given)' error for RoutablePage previews
Changelog for #818
Release note for #818
Merge pull request #811 from gasman/fix/catch-missing-images

Render missing images within rich text as broken images, rather than throwing IOError during rendering
Merge remote-tracking branch 'torchbox/stable/0.8.x'

Pulling #811 into master