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
Port OC_Property Table Index
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