With ANYPS5_FREE_SPACE=host, creating a save first checks the free space of
the save directory's volume against the save's size, 16384 blocks when the
title passes none. A save that does not fit fails with NO_SPACE_FS and
reports the blocks missing in required_blocks, and no directory is made.
If the volume cannot be queried, the create keeps today's behaviour and one
line goes to stderr. Opening an existing save and the default fixed mode are
unchanged.