On Windows, User ID/Group ID is not a number, so we ignore any parsing error
that may come from attempting to convert it to an integer. It will simply be '0'.
Don't defer the process Release until we have checked the error.
Skip the SIGHUP connection attempt on Windows. If the process exists, we assume it is running.
Since backend.ID is always a slice of constant length, use an array
instead of a slice. Mostly, arrays behave as slices, except that an
array cannot be nil, so use `*backend.ID` insteaf of `backend.ID` in
places where the absence of an ID is possible (e.g. for the Subtree of a
Node, which may not present when the node is a file node).
This change allows to directly use backend.ID as the the key for a map,
so that arbitrary data structures (e.g. a Set implemented as a
map[backend.ID]struct{}) can easily be formed.
