Fix issue where fetch's upstream data version causes txns we are waiting acks for, are ignored, causing re-sending of txns.

Fix is to check if txnQueue is non-empty, and to only load data and callback to
app when the last txnQueue item (at that moment in time) is removed from our txnQueue
Ensure that _x is not considered a subpath of _xs
null checking
make sure code can be minified always
Add failing test - filter on sorted filter does not emit transitively
Fix for last failing test - transitive emit works on filter of sorted filter results
Merge branch 'master' of github.com:codeparty/racer
Merge pull request #7 from codeparty/master

Pull upstream changes