Fix strings.c endian issue and strings test

Fix strings.c endian issue and strings test

git commit 71f5e3f7b624 obviously wasn't tested on a big-endian host,
and the test fail message resulted in tcl errors.

	* strings.c (unget_part_char): New function.
	(print_strings): Use unget_part_char.  Formatting.
	* testsuite/binutils-all/strings.exp (test_multibyte): Don't
	use square brackets in fail message.  Expect "String1\nString2".