* dbus/dbus-keyring.c: finish most of this implementation and
	simple unit test

	* dbus/dbus-errors.c (dbus_set_error_const, dbus_set_error): make
	these barf if the error isn't cleared to NULL

	* dbus/dbus-sysdeps.c (_dbus_delete_file): set error on failure
	(_dbus_create_directory): new function

	* dbus/dbus-errors.c (dbus_set_error): fix warning

	* dbus/dbus-string.c (_dbus_string_hex_encode): new function
	(_dbus_string_hex_decode): new function
	(test_hex_roundtrip): test code

	* dbus/dbus-sha.c (_dbus_sha_compute): use dbus_string_hex_encode

	* dbus/dbus-md5.c (_dbus_md5_compute): use dbus_string_hex_encode

	* dbus/dbus-sysdeps.c (_dbus_string_save_to_file): make this use
	the save-to-temp/rename trick to atomically write the new file
	(_dbus_string_parse_uint): new function