First try at fixing issue #185 fixes RELS-EXT but has causes side effects:
there are next/previous buttons when viewing master_files, which were
supposed to navigate within the unit -- they now only nav. within component.
We need to make this contect dependent. This seems to have been a design
error in original: next/prev should be attributes of the sequence (unit|component),
not master_file methods.
rollback: this change had other side-effects/breakage
Redo fix for next/previous problem (issue #185)
This time restrict it to RELS-EXT production in hydra.rb instead
of global change to master_files model to avoid other side-effects.
Merge branch 'issue-185'
fix issue #185 previous/next for generating components and master_files RELS_EXT