upgrade to ScalaCheck 1.11.0

for now this requires a special snapshot build of ScalaTest.
we shouldn't merge this until that has been sorted out.
see https://github.com/scalatest/scalatest/issues/181
Merge branch 'headless' into scalacheck-1.11

Conflicts:
	build.sbt
upgrade to ScalaCheck 1.11.2
upgrade to ScalaTest 2.1.RC1
upgrade to ScalaCheck 1.11.3
upgrade to ScalaTest 2.1.0-RC2
Merge branch 'headless' into scalacheck-1.11