Option to leave screen on and show status/previous picture during bulb exposure

Created originally on Bitbucket by dmilligan (David Milligan)

Was already merged in Bitbucket before import, marked as merged by the import user

Source changeset not longer availableat the time of import. Commit listwill look empty

Added a way to disable ML's turning off of the screen during bulb exposures. This allows the previously taken pic and intervalometer info to be shown on the screen during a bulb sequence that has little or no time between shots. Tested on 60D and 1100D.

I've kept this to myself b/c I wasn't sure of the likelihood of it getting merged. But I've found it extremely useful, so I thought I'd at least give it a shoot, b/c I think other users would find it useful as well.