Catch preupgrade exception

Backport of 1710cc14f63d2a8197ed340368f1f7c7c3193ed1 from master
Lock retry usleep requires milliseconds

Convert the milliseconds wait interval value to microseconds in the
files locking app

Backport of 0557dfb46f462d925aaa5cb6537cc92bb73e2f31 to stable7
Fix copy operation

Do not use locks when moving or copying folders to avoid creating empty
files.

Moved is_dir() check to the storage wrapper's rename() and copy() methods.
Now using $this->storage for the is_dir() check.

Removed clearstatcache() which does not seem to be needed any more when
using $this->storage.
Save the locked handle in obtainWriteLock
Updated info.xml app description

Updated app description. backporting to stable 7
Updated info.xml app description

Updated app description
Updated info.xml app description

backporting update to stable 7
Merge branch 'stable7-upstream' into stable7