Much simpler way to implement required UUIDs.  Just remove the methods/properties/constants every time it's called again.  Thanks @subvertallchris !
Make sure this happens when there's a session
Rescue from issues when dropping a constraint.  In my DB with 8 million nodes for a particular label, adding a constraint takes 141 seconds and it seems to be asynchronous for some reason...
Use UUIDs in query/query_proxy methods
Whoops, conflated variables here
Merge branch 'master' into require_uuid
UUIDs aren't created as sorted
Cover undef_property
Need to include the middle node so that the sorts can compare properly
If the constraint already exists, don't remove it
Merge pull request #478 from neo4jrb/require_uuid

Much simpler way to implement required UUIDs.