mod_video: dynamically reload the vide after processing.
Set is_video_processing and is_video_broken flags in the medium record.
core: allow undefined files in media updates.
Merge branch 'master' of github.com:zotonic/zotonic
core: allow undefined file for z_media_archive:is_archived/2.
mod_admin: also show medium if no file defined, but mime type is defined.