Sage-Bootstrap

This is a utility library for dealing with third-party tarballs and
building Sage. You should never import anything from the actual Sage
library here, nor should you import anything from sage_bootstrap into
Sage (because this would reconfigure logging). They must be kept
separate.

Everything here must support Python 2.6, 2.7, and 3.3+. Use tox
(https://testrun.org/tox/latest/) to automatically run the tests with
all relevant Python versions. Tests are written as unittest, not as
doctests, because the library is not meant to be used interactively.
Note that the library comes with a setup.py file so that tox can test
it, but it is not meant to be installed to SAGE_LOCAL.

Command-line utilities must be able to run as part of a pipe | filter
chain. So you have to be careful about what you send to stdout. You
should use:

* print() for anything that is meant to be sent to the output pipe.

* log.info() for human-readable messages about the normal program
  flow.

