Logic for choosing directory to store files in in bitarchives could be improved

During fixing of bug 1564 a new setting was introduced that defines the minimum amount of space we require left in a directory.
However we still will not store a file in a directory unless the amount of space defined by the original setting the one that now defines when to listen is free.
The implementation is trivial:
Simply update
if (checkArchiveDir(dir)
&& (bytesFreeInDir > minSpaceLeft)
&& (bytesFreeInDir - requestedSize > minSpaceRequired))
to
if (checkArchiveDir(dir)
&& (bytesFreeInDir - requestedSize > minSpaceRequired))
in BitarchiveAdmin.getTemporaryPath()
Estimated time: ½md (to update the unit tests to this logic and a quick review)