scala: fix incorrect doc installation path and add 'src' as resource

Closes Homebrew/homebrew#28818.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Formula/scala.rb

@@ -6,12 +6,18 @@ class Scala < Formula
   sha1 '65d1ef6231b4f08444dd10a015d2d82ea5444486'
 
   option 'with-docs', 'Also install library documentation'
+  option 'with-src', 'Also install sources for IDE support'
 
   resource 'docs' do
     url 'http://www.scala-lang.org/files/archive/scala-docs-2.11.0.zip'
     sha1 '4194808c15c928e902e9e36dbaaab05ca660213f'
   end
 
+  resource 'src' do
+    url 'https://github.com/scala/scala/archive/v2.11.0.tar.gz'
+    sha1 'bc1e301741854424a2ed8949cc46fa9091bc1b46'
+  end
+
   resource 'completion' do
     url 'https://raw.githubusercontent.com/scala/scala-dist/27bc0c25145a83691e3678c7dda602e765e13413/completion.d/2.9.1/scala'
     sha1 'e2fd99fe31a9fb687a2deaf049265c605692c997'
@@ -23,13 +29,9 @@ class Scala < Formula
     man1.install Dir['man/man1/*']
     libexec.install Dir['*']
     bin.install_symlink Dir["#{libexec}/bin/*"]
-
     bash_completion.install resource('completion')
-
-    if build.with? 'docs'
-      branch = build.stable? ? 'scala-2.10' : 'scala-2.11'
-      (share/'doc'/branch).install resource('docs')
-    end
+    doc.install resource('docs') if build.with? 'docs'
+    libexec.install resource('src').files('src') if build.with? 'src'
 
     # Set up an IntelliJ compatible symlink farm in 'idea'
     idea = prefix/'idea'