rework our .travis.yml
Revert "drop some cruft from .travis.yml"

This reverts commit bfea2081a13db9df7e31a4f4e975c1c4a76c2356.

For some reason, travis now complains again if we don't set user.name and
user.email explicitly...?!

Conflicts:
	.travis.yml
nit! additional comments