#146 Import ContentHandler class correctly

[Tomohiko Kinebuchi]

docutils.writers.docutils_xml.TestXml class inherits xml.sax.ContentHandler, but ContentHandler class belongs to xml.sax.handler module, so docutils.writers.docutils_xml module should do import xml.sax.handler.ContentHandler and TestXml class should inherit that class.

In this case, no error exists since xml.sax.__init__ module accidentally imports ContentHandler.

[Takeshi KOMIYA]

+1: xml.sax.handler.ContentHandler is official place of ContentHandler. Please refer the Python docs:
https://docs.python.org/3.6/library/xml.sax.handler.html#xml.sax.handler.ContentHandler

[Günter Milde]

Fixed in r8240. Thanks for the report.