* tests/regression.at (Token definitions): Don't rely on

AT_PARSER_CHECK for data that contains backslashes.  It currently
uses 'echo', and 'echo' isn't portable if its argument contains
backslashes.  Problem found on OpenBSD 3.4.  Also, do not assume
that the byte '\0xff' is not printable in the C locale; it is,
under OpenBSD 3.4 (!).  Luckily, '\0x80' through '\0x9e' are
not printable, so use '\0x81' to test.