Add travis PEP8 checker

This follows #1133 by adding a build to travis (takes < 1 min) that checks for PEP8 errors (except for line > 80 chars).

Note that this is *not* passing and shouldn't be merge - as discussed in #1133, we are not yet PEP8-compliant.  This could be modified to only check those packages that are compatible, or we can count on Jenkins to check this for now, and wait to merge this until we've got everything PEP8-ified.