Merge branch 'bc/utf16-portability-fix'

The code and tests assume that the system supplied iconv() would always use BOM in its output when asked to encode to UTF-16 (or UTF-32), but apparently some implementations output big-endian without BOM. A compile-time knob has been added to help such systems (e.g. NonStop) to add BOM to the output to increase portability. * bc/utf16-portability-fix: utf8: handle systems that don't write BOM for UTF-16