HPCC-11897 Spaces in filenames should be allowed

While it might have been better not to allow them from the start (arguable),
it does not seem like a good idea to make it impossible to read files in 5.0
that were legally created with earlier versions...

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
(we don't recommend mixing clients within a system)