This helps support 2.5 settings where there are virtual files in the
tree but new files aren't created virtual.
It's also a prelude for #6815
There's currently no way of
- upgrading vfs plugins (a silent suffix->winvfs upgrade is attempted
once only, when moving to master)
- disabling vfs capabilities outright
Conflicts:
src/csync/csync_reconcile.cpp
src/csync/csync_update.cpp
src/libsync/syncengine.cpp
src/libsync/syncengine.h
Note: csync changes from 5e442f588e
are not included and will be fixed separately
Unfortunately to do this, the local update phase must write to the
database, creating a new side-effect and order dependency (local update
must run before remote update).
Otherwise a interrupted or unsuccessful download would mean that the
download-intend was forgotten. The next sync would reestablish the
virtual file instead.
