Before this fix GetFreeSpace returned math.MaxInt64 for remotes which
don't support reading free space, however this is used in various
comparison routines as a too large value, meaning that remotes of size
math.MaxInt64 were never being selected.
This fixes GetFreeSpace to return math.MaxInt64 - 1 so then can be selected.
It also fixes GetUsedSpace the same way however as the default for not
supported was 0 this was very unlikely to have ever caused a problem.
Nick Craig-Wood
1e1af46a12