Add sonatype snapshots repo.

So that we can PR validate against Scala snapshots.

Author: adriaanm

build.sbt

@@ -12,6 +12,9 @@ scalaXmlVersion := "1.0.0-RC6"
 // so we don't have to wait for sonatype to synch to maven central when deploying a new module
 resolvers += Resolver.sonatypeRepo("releases")
 
+// to allow compiling against snapshot versions of Scala
+resolvers += Resolver.sonatypeRepo("snapshots")
+
 // dependencies:
 libraryDependencies += "org.apache.ant"                 % "ant"            % "1.8.4"