Add new sass package based on less package.

packages/sass/package.js

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+Package.describe({
+  summary: "Sassy CSS pre-processor."
+});
+
+var sass = require('sass');
+var fs = require('fs');
+
+Package.register_extension(
+  "sass", function (bundle, source_path, serve_path, where) {
+    serve_path = serve_path + '.css';
+
+    try {
+      var contents = fs.readFileSync(source_path);
+      var css = sass.render(contents.toString('utf8'));
+      // NOTE: sass does not seem to return any sort of error. It just
+      // silently ignores bad sass code.
+
+      bundle.add_resource({
+        type: "css",
+        path: serve_path,
+        data: new Buffer(css),
+        where: where
+      });
+    } catch (e) {
+      // Haven't been able to get sass to throw, but just in case.
+      bundle.error(source_path + ": Sass compiler error: " + e.message);
+    }
+  }
+);
+
+Package.on_test(function (api) {
+  api.add_files(['sass_tests.sass', 'sass_tests.js'], 'client');
+});

packages/sass/sass_tests.js

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+
+Tinytest.add("sass - presence", function(test) {
+
+  // find the .sass stylesheet, whose first rule contains "sass-tests"
+  // in the selector
+  var sheet = _.find(document.styleSheets, function(sh) {
+    var rules = sh.cssRules || sh.rules;
+    return /sass-tests/.test(rules[0].selectorText);
+  });
+
+  test.isTrue(sheet);
+
+  // `cssRules` is the W3C name, but isn't supported in IE until
+  // version 9.  IE<=8 has `rules`.  We prefer `cssRules` as
+  // it is less likely to have quirks if both are present.
+  var rules = sheet.cssRules || sheet.rules;
+
+  test.equal(rules[1].style.borderLeftWidth, "13px");
+});
+

packages/sass/sass_tests.sass

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+#sass-tests
+  :zoom 1
+
+unlucky: 13px
+
+.unlucky-left-border
+  :border-left-width !unlucky