Test for the new datastream ID truncation function is now working.
Found a bug in the revised datastream ID truncation algorithm: if an id which was too
long (>64) also started with an illegal character (initial characters have to be alpha
numeric), the 'D' prepended was pushing the length > 64.
Corrected the test fixtures to allow for the revision to the datastream-id
truncation algorithm.

All tests passing.