xmltwig/t/test_autoencoding_conversion.t treats PERL_UNICODE=SA as special

[DrHyde]

The order of letters in PERL_UNICODE is not important, so AS should be treated the same. Also other letters may be present so you should be checking for the presence of both letters, possibly with other letters in between, eg SDA or ADS. Actually it may be that only one of them matters, but regardless, treating only SA as special is wrong.