[Sass] Make sure empty lines in comments are included in the output.

Closes gh-12

lib/sass/engine.rb

@@ -170,7 +170,10 @@ module Sass
       lines = []
       string.gsub(/\r|\n|\r\n|\r\n/, "\n").scan(/^.*?$/).each_with_index do |line, index|
         index += (@options[:line] || 1)
-        next if line.strip.empty?
+        if line.strip.empty?
+          lines.last.text << "\n" if lines.last && lines.last.comment?
+          next
+        end
 
         line_tab_str = line[/^\s*/]
         unless line_tab_str.empty?

lib/sass/tree/comment_node.rb

@@ -50,9 +50,13 @@ module Sass::Tree
     def to_s(tabs = 0, _ = nil)
       return if invisible?
 
+      content = (value.split("\n") + lines.map {|l| l.text})
+      content.map! {|l| (l.empty? ? "" : " ") + l}
+      content.first.gsub!(/^ /, '')
+      content.last.gsub!(%r{ ?\*/ *$}, '')
+
       spaces = '  ' * (tabs - 1)
-      spaces + "/* " + (value.split("\n") + lines.map {|l| l.text}).
-        map{|l| l.sub(%r{ ?\*/ *$},'')}.join(style == :compact ? ' ' : "\n#{spaces} * ") + " */"
+      spaces + "/* " + content.join(style == :compact ? '' : "\n#{spaces} *") + " */"
     end
 
     # Returns `true` if this is a silent comment

test/sass/engine_test.rb

@@ -770,6 +770,19 @@ a
 SASS
   end
 
+  def test_empty_line_comment
+    assert_equal(<<CSS, render(<<SASS))
+/* Foo
+ *
+ * Bar */
+CSS
+/*
+  Foo
+
+  Bar
+SASS
+  end
+
   private
   
   def render(sass, options = {})