shared repository - add a few missing calls to adjust_shared_perm().

There were a few calls to adjust_shared_perm() that were
missing:

 - init-db creates refs, refs/heads, and refs/tags before
   reading from templates that could specify sharedrepository in
   the config file;

 - updating config file created it under user's umask without
   adjusting;

 - updating refs created it under user's umask without
   adjusting;

 - switching branches created .git/HEAD under user's umask
   without adjusting.

This moves adjust_shared_perm() from sha1_file.c to path.c,
since a few SIMPLE_PROGRAM need to call repository configuration
functions which in turn need to call adjust_shared_perm().
sha1_file.c needs to link with SHA1 computation library which
is usually not linked to SIMPLE_PROGRAM.

Signed-off-by: Junio C Hamano <junkio@cox.net>

refs.c

@@ -104,6 +104,11 @@ int create_symref(const char *git_HEAD, const char *refs_heads_master)
 		error("Unable to create %s", git_HEAD);
 		return -3;
 	}
+	if (adjust_shared_perm(git_HEAD)) {
+		unlink(lockpath);
+		error("Unable to fix permissions on %s", lockpath);
+		return -4;
+	}
 	return 0;
 }