Allow mixins to take precedence over sibling selectors in ambiguous cases.

lib/sass/engine.rb

@@ -251,7 +251,7 @@ END
       when MIXIN_DEFINITION_CHAR
         parse_mixin_definition(line)
       when MIXIN_INCLUDE_CHAR
-        if line.text[1].nil? || line.text[1] == ?\s
+        if line.text[1].nil?
           Tree::RuleNode.new(line.text, @options)
         else
           parse_mixin_include(line, root)

test/sass/engine_test.rb

@@ -336,7 +336,6 @@ SASS
   end
 
   def test_mixins_dont_interfere_with_sibling_combinator
-    assert_equal("foo + bar {\n  a: b; }\n", render("foo\n  + bar\n    a: b"))
     assert_equal("foo + bar {\n  a: b; }\nfoo + baz {\n  c: d; }\n",
                  render("foo\n  +\n    bar\n      a: b\n    baz\n      c: d"))
   end