Log UserErrors on a higher level
Currently UserErrors are logged as a debug info [1], but this errors contain the traceback which is useful to help the user to determine which is the cause of the error.
So it will be great if they can raise a WARN instead of and error, so with the WARN level we can get a log with all the errors raised by the application.
This goes in concordance with the logging howto [2] as the application can do nothing about the situation, but it's great to note it.
[1] http://hg.tryton.org/trytond/file/tip/trytond/protocols/dispatcher.py#l214
[2] https://docs.python.org/2.7/howto/logging.html?highlight=logger