VfsSuffix: Wipe stale pin states #7273
Previously the pin states of deleted files stayed in the 'flags'
database and could be inadvertently reused when a new file with the same
name appeared. Now they are deleted.
To make this work right, the meaning of the 'path' column in the 'flags'
table was changed: Previously it never had the .owncloud file suffix.
Now it's the same as in metadata.path.
This takes the safe parts from #7274 for inclusion in 2.6. The more
elaborate database schema changes (why use 'path' the join the two
tables in the first place?) shall go into master.