progress: drop extra args for pos=None calls (issue2087)

check-code: fix check-code complaint

check-code: improve quote detection regexp, add tests

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.