Use vertex0 when computing neutral candidates directions for isolation computation.

The option is on by default.
Using packedCandidate vertex makes inner veto ineffective.
Seems to be related to neutral packed candidates with displaced vertexes, most likely from conversions.

Attached plot shows
![neutralvtxforiso](https://cloud.githubusercontent.com/assets/638761/5226236/cb1ecd9a-76ec-11e4-9dc0-beb5599d4ac2.png)
 the effect.