Fix bug in long name handling.
Fix bug in long name handling.

The code handling long names failed when the "Millisecond stamp at
file creation time" field (byte 13 of the short name directory entry)
happened to be the same value as the checksum of the short name
directory entry. (Random chance uncovered this error in my test file
system image. Would never had thought to test for it.) Rewrote name
handling to more obviously follow the spec.

froggey/Mezzano,froggey/Mezzano