pathspec: add flag to indicate operation without repository

pathspec: add flag to indicate operation without repository

A following change will add support for pathspecs to the git diff
--no-index command. This mode of git diff does not load any repository.

Add a new PATHSPEC_NO_REPOSITORY flag indicating that we're parsing
pathspecs without a repository.

Both PATHSPEC_ATTR and PATHSPEC_FROMTOP require a repository to
function. Thus, verify that both of these are set in magic_mask to
ensure they won't be accepted when PATHSPEC_NO_REPOSITORY is set.

Check PATHSPEC_NO_REPOSITORY when warning about paths outside the
directory tree. When the flag is set, do not look for a git repository
when generating the warning message.

Finally, add a BUG in match_pathspec_item if the istate is NULL but the
pathspec has PATHSPEC_ATTR set. Callers which support PATHSPEC_ATTR
should always pass a valid istate, and callers which don't pass a valid
istate should have set PATHSPEC_ATTR in the magic_mask field to disable
support for attribute-based pathspecs.

Signed-off-by: Jacob Keller <jacob.keller@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>