Issue 780: HasNavigationPropertyLink doesn't allow replace existing link
builder
Issue 776: Null argument exception when trying to return an entry with a
custom edit link in minimal metadata mode

we were comparing the generated self-link and the generated edit link and
not emit edit link in minimal metadata modes if they are the same. This
check is expensive to perform consistently in all cases and is also the
cause of this bug.
Fixing it by not doing this comparison. This also has the nice side effect
that telling your edit link is the same as id link can be done in one
consistent way i.e. by not setting the edit link factory.