[PATCH/RFC 0/2] fix some rev-parse options in non-repos

Michael Haggerty noticed recently (off-list) that "git rev-parse --local-env-vars" doesn't work outside of a git repository. This turns out to be a regression in v1.8.5, due to a patch by John Keeping that lifted some other restrictions on how the option could be used.

This fixes it by reverting John's patch, which puts the original restrictions back in place. I won't repeat the lengthy discussion from patch 2's commit message here, but the gist of it is that probably nobody cares about those restrictions, it's more important to fix the original regression, and it's probably too hard to make both work.

The only thing that gives me pause (and hence the RFC) is that it has been over 2 years since the original regression. So it's entirely possible somebody will consider _this_ fix a regression.

  [1/2]: t1515: add tests for rev-parse out-of-repo helpers
  [2/2]: Revert "rev-parse: remove restrictions on some options"

-Peff