The changes cause compilation failures in any file in the Python
installation lib directory to cause the install to fail.  It looks
like compileall.py intended to behave this way, but a change to
py_compile.py and a separate bug defeated it.

Fixes SF bug #412436

This change affects the test suite, which contains several files that
contain intentional errors.  The solution is to extend compileall.py
with the ability to skip compilation of selected files.

NB compileall.py is changed so that compile_dir() returns success only
if all recursive calls to compile_dir() also check success.