Fixed focal point indicator positioning

The focal point indicator is always positioned as a percentage inside
the div.focal-point-chooser block.

For thin images, the image may not exactly fill this block causing the
indicated focal point to be too wide and often not even cover the image.

This commit fixes this by making sure the width and height of the
div.focal-point-chooser block are always the same as the image, even if
the image is too small.
add missing south migration - remove auto_add_now from page_revision.created_at and nullify page owner on user deletion
add migration to tests app to fix typo in formfield help text. (Most. Pointless. Migration. Ever.)
Add dependency on wagtailcore migration 0002 (necessary to cleanly merge the other migration 0005 being added in 0.9)
Fix some more python3.2-incompatible unicode strings in migration 11
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
Merge branch 'image-focal-point-chooser-fixes' of https://github.com/kaedroho/wagtail into kaedroho-image-focal-point-chooser-fixes
Release note for #807
Merge branch 'kaedroho-image-focal-point-chooser-fixes'
Renames duplicate method on TestSnippetRegistering
Fix 'TypeError at /admin/pages/ID/edit/preview/ serve_subpage() takes exactly 2 arguments (1 given)' error for RoutablePage previews
Merge pull request #817 from salvadormrf/master

Renames duplicate method on TestSnippetRegistering
Use request instead of self
Merge remote-tracking branch 'zerolab/routable-preview'
Changelog for #818
Release note for #818
Fix 'TypeError at /admin/pages/ID/edit/preview/ serve_subpage() takes exactly 2 arguments (1 given)' error for RoutablePage previews