Without this, when an index update comes in we only do a new pull if the
remote `localVersion` was increased. But it may not be, because the
index is sent alphabetically and the file with the highest local version
may come first. In that case we'll never do a new pull when the rest of
the index comes in, and we'll be stuck in idle but with lots of out of
sync data.
The "Invalid" config attribute is retained for errors discovered during
config loading (empty path, duplicate ID). This can only be set or
cleared at config loading time.
Errors discovered during runtime (I/O problems, etc) are now in the
folder state instead. Changes to these are sent as any other folder
state change.
