.gitattributes lookup doesn't respect GIT_WORK_TREE

The functions in attr.c do not look at $GIT_WORK_TREE when trying to
find the .gitattributes file.  Thus if you are not inside the work tree,
but have GIT_WORK_TREE set attribute lookup will be wrong.

Password Store <http://www.passwordstore.org/> is using this feature
when the password store is a git repository.  It sets up a diff
attribute that decrypts the contents, but that works only if the command
is issued while inside the repository.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."