Imported modules now have __builtins__ set.

In the past Jython did not support __builtins__ as an implementation
detail of CPython. See for example
https://docs.python.org/2/library/__builtin__.html and
http://bugs.jython.org/issue1890. However, we might as well support
it, since doing so further minimizes compatibility differences.

Also updated test_builtin and test_module to latest version from 2.7,
then applied a minimal set of Jython-specific changes. Removed
Jython-specific test_pdb