Issue title: Ubuntu15.04 fcitx候选字体有阴影
 Issue body: Ubuntu15.04 fcitx候选字体有阴影
![img_20150505_074637](https://cloud.githubusercontent.com/assets/7426281/7466100/ec954446-f30f-11e4-8093-65cd891403e5.jpg)

 Comments: 
 Comment 0: 感觉是显卡驱动问题…
 Comment 1: 跑一下fcitx-diagnose?
{'source': 'GithubIssues', 'repo_name_with_owner': 'fcitx/fcitx', 'issue_id': 73180660, 'repo_stars': 777.0}