Switch to SBT 0.13 source position mapper

SBT 0.13 added a source position mapper feature, so that we didn't have
to parse compile errors from the logs anymore.  This change removes all
that complex logic, and replaces it with a simple setting for SBT.

In addition, I've implemented a scripted test to verify that it works.
Merge pull request #1455 from jroper/source-position-mapper

Switch to SBT 0.13 source position mapper