WORKING ON IT:    Trying to get roundtrip conversion working
COMMENTS

REMOVE WHEN IT WORKS
po2idml: Skip first unit when retrieving translated units

This doesn't apply on XLIFF because all units have a source, but in PO
the first unit parsed is the one in the PO header, which has blank source.
idml2po: Record in unit location the file within the IDML it was extracted from

This records a second location on each unit, besides the other location
used to keep the xpath.

This is necessary because the files we are extracting from the IDML packages
have the same root tag, where the ODF packages have a different root tag
for each of the translatable files we extract.

This change doesn't require any alterations in the ODF converters.
WORKING: Change required to get the translatable files

This is necessary to be able to group the translated units per translatable
file, and thus build the XPathTree objects for each of them.
UNDO