Use a context manager instead of calling _test.run in multiple places. Alleviates need to warn about Exceptions

On Python 3.3+, `find_packages()` now considers any subdirectory of the
start directory that's not a regular package (i.e., that doesn't have an
`__init__.py`) to be a namespace package. Because this will often
include non-package directories, a new `include` argument has been added
to `find_packages()`.

`include` can make it easier to narrow which directories are considered
packages instead of having to specify numerous excludes. In
particular, it's an easy way to keep top-level, non-source directories
from being considered packages.

The other way this supports PEP 420 is by making sure `__pycache__`
directories are never added to the list of packages.

Refs issue #97

On Python 3.3+, `find_packages()` now considers any subdirectory of the
start directory that's not a regular package (i.e., that doesn't have an
`__init__.py`) to be a namespace package.

The other way this supports PEP 420 is by making sure `__pycache__`
directories are never added to the list of packages.

Fixes issue #97

--HG--
extra : rebase_source : bee4238f4cd00fa8bd3104017f4caf234dcf0729

--HG--
extra : rebase_source : 1fec39a038ac2c460e62ef2ee2eee5a0b66a676d

--HG--
extra : rebase_source : 3b48a37ada247203bfebf87cdbb473b72e6e208b

--HG--
extra : rebase_source : fecc027e4355f36d779967683a213fb2d867d21a