avoid duplicate classes during transclusion (fix #1806)

Author: yyx990803

src/compiler/transclude.js

@@ -141,8 +141,9 @@ function mergeAttrs (from, to) {
     if (!to.hasAttribute(name) && !specialCharRE.test(name)) {
       to.setAttribute(name, value)
     } else if (name === 'class') {
-      value = to.getAttribute(name) + ' ' + value
-      to.setAttribute(name, value)
+      value.split(/\s+/).forEach(function (cls) {
+        _.addClass(to, cls)
+      })
     }
   }
 }

test/unit/specs/compiler/transclude_spec.js

@@ -112,13 +112,13 @@ if (_.inBrowser) {
     })
 
     it('replacer attr should overwrite container attr of same name, except class should be merged', function () {
-      el.setAttribute('class', 'test')
+      el.setAttribute('class', 'test other')
       el.setAttribute('title', 'parent')
-      options.template = '<div class="other" title="child"></div>'
+      options.template = '<div class="other ok" title="child"></div>'
       options.replace = true
       options._asComponent = true
       var res = transclude(el, options)
-      expect(res.getAttribute('class')).toBe('other test')
+      expect(res.getAttribute('class')).toBe('other ok test')
       expect(res.getAttribute('title')).toBe('child')
     })