When setup_git_directory() is called, we set a flag in
startup_info to indicate we have a repository. But there are
a few other mechanisms by which we might set up a repo:
1. When creating a new repository via init_db(), we
transition from no-repo to being in a repo. We should
tweak this flag at that moment.
2. In enter_repo(), a stricter form of
setup_git_directory() used by server-side programs, we
check the repository format config. After doing so, we
know we're in a repository, and can set the flag.
With these changes, library code can now reliably tell
whether we are in a repository and act accordingly. We'll
leave the "prefix" field as NULL, which is what happens when
setup_git_directory() finds there is no prefix.
Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>