[Owncloud] Fix for upgrade with files app

[Arthur Schiwon]

Hey,

just want to let you know, that i commited a fix [1] to master that 
tries to remove everything but web.dav from the /files folder to make an 
upgrade from 3 to 4 possible. Imho pretty critical for the release. If 
deleting fails, it will only display a log message including a hint for 
that admin what to remove. Hope that's enough of user info.

Cheers
Arthur

[1] 
https://gitorious.org/owncloud/owncloud/commit/fbc2892083c03329d4c64544a79ce143a97ce6bd