Fixes Typo

see https://github.com/warner/python-versioneer/blob/master/src/cmdclass.py#L68
Remove trailing whitespace from git/install.py
cleanups in prep for new script-only code

no behavioral changes, just lining up the test harness to make the next
commit cleaner
make it possible to use on script-only packages

These packages have no modules (e.g. setup.py has packages=[]), so they
can't import a MODULE/_version.py . Instead, their setup.py's
"build_scripts" command has been overridden to interpolate a version
string into a generated scripts= file.

To use versioneer on script-only packages, set versionfile_build=None
fix py2-vs-3 problems in new tests
script-only: don't create a new __init__.py

This should remove the weirdness that happens when _version.py doesn't
have an __init__.py next to it.
release 0.12
setup.py: bump version to 0.12+ while between releases

also add notes about bdist_wheel debugging