Integrate sbt-mima-plugin.
Backport changes on 2.2.x_2.10 branch.
Merge branch '2.2.x_2.9' into 2.2.x_2.10

Conflicts:
	atmosphere/src/main/scala/org/scalatra/atmosphere/ScalatraAtmosphereHandler.scala
	commands/src/main/scala/org/scalatra/commands/executors.scala
	core/src/main/scala/org/scalatra/FutureSupport.scala
	core/src/main/scala/org/scalatra/ScalatraBase.scala
	core/src/test/scala/org/scalatra/ContentTypeTest.scala
	scalate/src/main/scala/org/scalatra/scalate/ScalateSupport.scala
	scalate/src/test/scala/org/scalatra/scalate/ScalateFuturesSupportSpec.scala
Merge branch '2.2.x_2.10' into 2.3.x_2.10