bugfix: don't print length as a Uint after request data.

This seems like it was a parenthesization error – what was intended
was likely this:

	write(pd(parser).data, bytestring(convert(Ptr{Uint8}, at), len))

rather than what was written, which was this:

	write(pd(parser).data, bytestring(convert(Ptr{Uint8}, at)), len)

However, there's no need to construct a ByteString at all since we
just want to copy a bunch of bytes between spots in memory.