Revert "Correctly insert at an existing parent if appropriate"

This reverts commit bb04ce073bfd5e1543285074b20fedf54d3f6feb.

Tests are failing because of this change. Nothing seems wrong with the
change but it needs a fix to the related tests before it lands again.
docs: add ref for intersphinx links
roundtrip: run silently when roundtripping
Merge accelerators in Mozilla .properties files

Fixes bug 115.
Simplify tests

After the previous commit, TestProp2PO.prop2po() can take an optional
personality kwarg, so use that.