1) super files calculate the common shared directory and set the file descriptor to use it, and set parts overrite to be the distinct tail.
The introduction of the dir-per-part flag, caused super part filenames to have the part-per-part subdir added twice.
Fix: since it is precalculated (via overridename) in super case, deliberately turn off flag when fetching the super file descriptor

2) Deseriazliaing a IFileDescriptor from xml was picking up the new file flags (which determines dir-per-part) from the wrong place.
Fix: pick up from Attr/