Merge branch '7.x-solution-pack-viewer-whitescreen' of https://github.com/nigelgbanks/islandora into 7.x
allow mulitple mime types for viewers
Merge branch '7.x' of git://github.com/Islandora/islandora into 7.x
Merge branch '7.x' of git://github.com/Islandora/islandora into 7.x
Merge branch '7.x-hookable-metadata' of github.com:jordandukart/islandora into 7.x
Merge branch '7.x' of git://github.com/Islandora/islandora into 7.x
Merge branch '7.x' of git://github.com/Islandora/islandora into 7.x
remove comment
docs update for array of mime types
spelling
cs fixes
Make the "undo_function" bit optional.

The "undo_function" part of callbacks was required, even though it
might not be required for functionality... Make it optional, so we
don't end up making/using no-op functions to avoid doing anything.
Merge remote-tracking branch 'origin/7.x' into 7.x-USDA-41
Merge pull request #473 from adam-vessey/7.x-USDA-41

Make the "undo_function" bit optional.
passing derivative deffinition to callback (usefull for single callback handling many derivatives)
forgot comma
Merge pull request #477 from willtp87/7.x.derivative_args

passing derivative deffinition to callback (usefull for single callback ...
Don't render unneeded markup when there is no thumbnail.
Merge pull request #478 from jordandukart/7.x-default-object-markup

Don't render unneeded markup when there is no thumbnail.
Grab latest PHPCS as Coder now supports it.