[PATCH 0/5] credential helper super fun pak

Here's a mixed bag of bugfix commits to go on top of what's in jk/http-auth-keyring.

  [1/5]: docs: minor tweaks to credentials API

    Clarifications in response to comments from Junio on the original
    series.

  [2/5]: credential-cache: fix expiration calculation corner cases

    This fixes the failures in t0300 on OS X.

  [3/5]: t0300: make askpass tests a little more robust
  [4/5]: t0300: make alternate username tests more robust

    These two just make the tests more rigorous so that patch 5/5
    can actually demonstrate the failure it's fixing.

  [5/5]: credential-store: use a better storage format

    This makes multiple usernames on the same host work with
    credential-store (they already work with credential-cache).

-Peff