Add "get_sha1()" helper function.

This allows the programs to use various simplified versions of
the SHA1 names, eg just say "HEAD" for the SHA1 pointed to by
the .git/HEAD file etc.

For example, this commit has been done with

	git-commit-tree $(git-write-tree) -p HEAD

instead of the traditional "$(cat .git/HEAD)" syntax.

1 files changed, 1 insertions, 1 deletions

diff --git a/tar-tree.c b/tar-tree.c
index ea7ea91..2c64f69 100644
--- a/tar-tree.c
+++ b/tar-tree.c
@@ -338,7 +338,7 @@ int main(int argc, char **argv)
 		basedir = argv[2];
 		/* FALLTHROUGH */
 	case 2:
-		if (get_sha1_hex(argv[1], sha1) < 0)
+		if (get_sha1(argv[1], sha1) < 0)
 			usage(tar_tree_usage);
 		break;
 	default: