proxy: don't pass arguments to format_exc() in IkiWikiProcedureProxy.run()
This avoids:
Traceback (most recent call last):
File "./plugins/rst", line 86, in <module>
proxy.run()
File "/home/wking/src/ikiwiki/plugins/proxy.py", line 316, in run
e, traceback.format_exc(sys.exc_info()[2])))
File "/usr/lib/python3.2/traceback.py", line 269, in format_exc
...
TypeError: unorderable types: int() < traceback()
The syntax for format_exc in Python 2.x is:
traceback.format_exc([limit])
In Python 3.x, it is:
traceback.format_exc(limit=None, chain=True)
Neither of these need any information from sys.exc_info() passed in.