SSL.File: Use an IOBuffer to buffer write()'s.

This changes the write_buffer implementation from using an array(string)
to using IOBuffer.

Caveat: It is unknown whether this is dead-lock free in
        threaded blocking mode.
Remove redundant check.
Added some __deprecated__
Better debug.
Fixed the decoder callback prototype and the Sequence decode_primitive (is this every called?)
Removed add_byte. We have add_int8.