Merge branch 'jk/quote-env-path-list-component' into next

Merge branch 'jk/quote-env-path-list-component' into next

A recent update to receive-pack to make it easier to drop garbage
objects made it clear that GIT_ALTERNATE_OBJECT_DIRECTORIES cannot
have a pathname with a colon in it (no surprise!), and this in turn
made it impossible to push into a repository at such a path.  This
has been fixed by introducing a quoting mechanism used when
appending such a path to the colon-separated list.

* jk/quote-env-path-list-component:
  t5547-push-quarantine: run the path separator test on Windows, too
  tmp-objdir: quote paths we add to alternates
  alternates: accept double-quoted paths