Add sbt (scala build tool) package

var/spack/repos/builtin/packages/sbt/package.py

+from spack import *
+import shutil
+
+
+class Sbt(Package):
+    """Scala Build Tool"""
+
+    homepage = "http://http://www.scala-sbt.org"
+    url      = "http://http://www.scala-sbt.org/download.html"
+
+    version('0.13.12', 'cec3071d46ef13334c8097cc3467ff28',
+            url='https://dl.bintray.com/sbt/native-packages/sbt/0.13.12/sbt-0.13.12.tgz')
+
+    depends_on('jdk')
+
+    def install(self, spec, prefix):
+        shutil.copytree('bin', join_path(prefix, 'bin'), symlinks=True)
+        shutil.copytree('conf', join_path(prefix, 'conf'), symlinks=True)