for-each-repo: test outside of repo context

for-each-repo: test outside of repo context

The 'git for-each-repo' tool is frequently run outside of a repo context
in the real world. For example, it powers background maintenance.
Despite this typical case, we have not been testing it without a local
repository.

Update t0068 to stop creating a test repo and to use global config
everywhere. This has some subtle changes to test across the file.

This was noticed because an earlier attempt to remove the_repository
from builtin/for-each-repo.c did not catch a segmentation fault since
the passed 'repo' is NULL. This use of the_repository will need to stay
until we have a better way to handle config queries outside of a repo
context. Similar use still exists in builtin/config.c for the same
reason.

Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>