Added msg to docstring for cleaning pyc.
Added msg to docstring for cleaning pyc.

nicoddemus/pytest,RonnyPfannschmidt/pytest,alfredodeza/pytest,tomviner/pytest,Akasurde/pytest,The-Compiler/pytest,The-Compiler/pytest,nicoddemus/pytest,markshao/pytest,pytest-dev/pytest,tomviner/pytest