hash-object: always try to set up the git repository

When "hash-object" is run without "-w", we don't need to be in a git repository at all; we can just hash the object and write its sha1 to stdout. However, if we _are_ in a git repository, we would want to know that so we can follow the normal rules for respecting config, .gitattributes, etc. This happens to work at the top-level of a git repository because we blindly read ".git/config", but as the included test shows, it does not work when you are in a subdirectory. The solution is to just do a "gentle" setup in this case. We already take care to use prefix_filename() on any filename arguments we get (to handle the "-w" case), so we don't need to do anything extra to handle the side effects of repo setup. An alternative would be to specify RUN_SETUP_GENTLY for this command in git.c, and then die if "-w" is set but we are not in a repository. However, the error messages generated at the time of setup_git_directory() are more detailed, so it's better to find out which mode we are in, and then call the appropriate function. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>