When converting strings to a sequence of bytes, we can't just cast chars to
ints, and write that, because non-ascii characters will resulting values
outside the byte range.
Instead explicitly convert the string to a UTF8 byte array, and process that.
https://bugzilla.xamarin.com/show_bug.cgi?id=56876
Rolf Bjarne Kvinge
Waleed Chaudhry
Zoltan Varga