Add unit test for edges with infinite weights

We set some edge weights to `POWER(0, -1)`, which is how we represent
infinity in SQL. I make sure this is interpreted as
`Double.POSITIVE_INFINITY` in Java by adding a unit test.

Setting an edge weight to infinity is equivalent to deleting it from the
graph.
Merge pull request #324 from agouge/dist-infinity

Add unit test for edges with infinite weights
We set some edge weights to `POWER(0, -1)`, which is how we represent
infinity in SQL. I make sure this is interpreted as
`Double.POSITIVE_INFINITY` in Java by adding a unit test.

Setting an edge weight to infinity is equivalent to deleting it from the
graph.

@gpetit This is what you were talking about yesterday.