Merge with stable

check-code: add a return value to checkfile function The checkfile function returns True if the file is correct, False otherwise.

code-code: Add a logfunc argument to checkfile This helps external tool customisation. The logfunc argument must be a function called to report errors. A new logger class is also added to keep the old behaviour by default.

check-code: Add a ``maxerr`` argument to the ``checkfile`` function check-code.py used to halt after 15 errors. This changeset adds a new argument to the checkfile function to control this limit.