V2EX没有检测上传图片类型，导致抛出错误，原因我虽然选择了svg类型的图片，但是还是上传了。 结果：

Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/tornado/web.py", line 1042, in _execute
getattr(self, self.request.method.lower())(*args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/tornado/web.py", line 1809, in wrapper
return method(self, *args, **kwargs)
File "/www/v2ex/galaxy/handlers/web/settings.py", line 373, in post
avatar73 = self.rescale(avatar, 73, 73)
File "/www/v2ex/galaxy/handlers/__init__.py", line 432, in rescale
img = pil.open(input_file)
File "/usr/lib/python2.7/dist-packages/PIL/Image.py", line 1980, in open
raise IOError("cannot identify image file")
IOError: cannot identify image file