It turns out that these two instructions are coming from the Scala compiler and so what needs to happen under the covers is for scalac to be called with -deprecation or -feature as described here:
http://www.scala-lang.org/files/archive/nightly/docs-2.10.3/manual/html/scalac.html
(actually I never saw the -feature option explained anywhere but I was able to specify it as follows)
I'm using the scala-maven-plugin and compiling with scala:compile described here:
http://davidb.github.io/scala-maven-plugin/compile-mojo.html
The relevant parameter is described here:
http://davidb.github.io/scala-maven-plugin/compile-mojo.html#addScalacArgs
So, two maven commands that I found helpful were:
mvn clean compile -DaddScalacArgs=-deprecation mvn clean compile -DaddScalacArgs=-feature