Install scala to libexec and link in "bin"

Homebrew policy is to avoid putting jars into "lib",
so moving Scala to a more idiomatic Java install.

Formula/scala.rb

@@ -8,7 +8,10 @@ class Scala <Formula
 
   def install
     rm_f Dir["bin/*.bat"]
+    doc.install Dir['doc/*']
     man1.install Dir['man/man1/*']
-    prefix.install Dir['*']
+    libexec.install Dir['*']
+    bin.mkpath
+    Dir["#{libexec}/bin/*"].each { |f| ln_s f, bin }
   end
 end