pypy: fix failing test-devel-warnings.t with Pypy5.6.0
In Pypy 5.6.0, traceback exception classes are not displayed with their full
qualified name.
Instead of displaying mercurial.error.ProgrammingError, Pypy displays
ProgrammingError.
Update the test to support both version.
pypy: fix failing test files with Pypy5.6.0
Pypy 5.6.0 saves cached bytecode files in __pycache__ directory, clean them in
tests to fix loading old test extensions code.
Doing so should also helps for Python3.x migration.