Add sass-spec test suite

.gitmodules

 [submodule "libsass"]
 	path = libsass
 	url = git://github.com/hcatlin/libsass.git
+[submodule "test/sass-spec"]
+	path = test/sass-spec
+	url = https://github.com/sass/sass-spec.git

sass-spec @ d516aefa

+Subproject commit d516aefa786f3cd3dd2914bb33d9760090176503

test/sass-spec.js

+var assert = require('assert'),
+    fs = require('fs'),
+    path = require('path'),
+    sass = require('../sass');
+
+var normalize = function(text) {
+  return text.replace(/\s+/g, '').replace('{', '{\n').replace(';', ';\n');
+};
+
+describe('sass-spec', function() {
+  var sassSpecPath = path.join(__dirname, 'sass-spec'),
+      sassSpecDirExists = fs.existsSync(sassSpecPath);
+
+  describe('test directory', function() {
+    it('it should exist', function() {
+      assert.ok(sassSpecDirExists);
+    });
+  });
+
+  if (sassSpecDirExists) {
+    var suitesPath = path.join(sassSpecPath, 'spec');
+    var suites = fs.readdirSync(suitesPath);
+    var ignoreSuites = ['todo', 'benchmarks'];
+
+    suites.forEach(function(suite) {
+      if (ignoreSuites.indexOf(suite) !== -1) {
+        return;
+      }
+
+      describe(suite, function() {
+        var suitePath = path.join(suitesPath, suite);
+        var tests = fs.readdirSync(suitePath);
+
+        tests.forEach(function(test) {
+          var testPath = path.join(suitePath, test);
+
+          it(test, function(done) {
+            sass.render({
+              file: path.join(testPath, 'input.scss'),
+              includePaths: [testPath, path.join(testPath, 'sub')],
+              success: function(css) {
+                var expected = fs.readFileSync(path.join(testPath, 'expected_output.css'), 'utf-8');
+
+                assert.equal(normalize(css), normalize(expected));
+                done();
+              },
+              error: function(error) {
+                done(new Error(error));
+              }
+            });
+          });
+        });
+      });
+    });
+  }
+});