incremental build testing

This small test tree is exercising incremental rebuild behavior in pants & sbt to see if our assumptions are being met.

project structure

src/main/scala/A/A.scala
- class A
src/main/scala/B/B.scala
- class B uses A internally

experiments

experiment	expectation	pants	sbt ~compile
change public signature of A	invalidate B	2	2
change private signature of A	don't invalidate B	2	1
change function body of A	don't invalidate B	2	1
change anything in B	don't invalidate A	1	1