Rearrange phase enhancement so that it handles phase errors in both directions.
This almost doubles the number of messages recovered by phase enhancement.
Merge pull request #36 from mutability/improve-phase-enhancement

Rearrange phase enhancement so that it handles phase errors in both directions
Merge branch 'master' of https://www.github.com/MalcolmRobb/dump1090
Merge branch 'master' into since