Fix lost ETag on Cache Upgrade
Performance: prepare queries only once
Upgrade FileCache on ownCloud upgrade for all users with files
Remove Debug output
Change LIMIT in DB query respectively remove where not necessary
Add Index to properties table for better performance on upgrade
Port Icewind's fix I
Cache: fix property path for getting legacy etag
Adjust to Icewind's fix
Add PHPDoc
Only prepare an SQL statement once.
Cache: Do not overwrite ETag when file did not change
Cache: on equal mtime also for equal size before keeping ETag, at least makes Unit Test happy
Merge pull request #2558 from owncloud/fix_cache_upgrade

Fix cache upgrade