Test compatibility reading from old index format.

Index format has subtly changed since 2.0.0
(numbers are written as string fields instead of numeric fields,
but using the same numeric format).
This test confirms that new code can read the old format.
Merge pull request #1798 from apcj/index-compat

Test compatibility reading from old index format.
Revert "CoreAPI getRelationships now delegates to kernel API."

This reverts commit e8043a30c78f88a75a5e0c106bd2d18356612adb.
due to heavy performance hit. Will make its way in at a later point.
Revert "Initial work on listing rels for a node via kernel API."

This reverts commit 81d75c3419560abea0e6333e43341168f31ff218.
Some initial porting from that old bloody branch