fixed rels
temporarily weakening taxon constraint for spiral organ,
moving to pending axioms file.
Addresses issue #387 (for now)
 aligning with MP: terminology for arcuate veins; NTs for endometrial vessels
typo
NTs for somite border and epithelium.
Does not seem satisfactory yet. What does the XAO class represent?
is it part of the initial somite, or the recently induced epithelium
from the PSM which will form the next somite?
Expert input sought