Improve Travis coverage
Rework travis (yet again) to do more testing per build. since tests are
concurrent we gain little by having some jobs take less time (except
a headstart on the next build)

Specifically:
- roll LOCALE_OVERRIDE into an extra step on one of the other jobs
- do "not slow" followed by full_deps install followed by "slow and not network" or just "slow",
  fail if either fail.

For example, right now "slow" tests that use 2.7 syntax should fail the build
but don't , since the 2.6 job doesn't run them.
