Merge remote-tracking branch 'breznak/modular-numpy' into politics

Conflicts:
	external/common/requirements.txt
Incorporating feedback from scott and others in order to get this branch approved.

Conflicts:
	build.sh
Triple verbosity and removing --target in favor of --prefix in --install-option
Removed popd from cleanUpEnv causing builds to fail.
Removing the now-redundant --install-scripts install option
Removing the --ignore-installed CLI option.  When present, numpy will always
re-compile/re-install which is not the desired behavior and by not specifying
it on the command line, the user can always override with either a pip config
file in $HOME, or by PIP_IGNORE_INSTALLED env variable.

Ultimately, we'll be getting rid of --find-links, --no-index, and --index-url
options too, so it makes sense to keep the pip command as light as possible.
Do a clean build in travis, set PIP_IGNORE_INSTALLED in cleanbuild.sh
Explicitly set PIP_IGNORE_INSTALLED in .travis.yml
Merge remote-tracking branch 'upstream/master' into politics