fuseOptions4 does not keep the option data type

For instance in #2917 (closed) the fusion of type=060, len=004: "1234" (string) and type=060, len=004: "5678" (string) gives the raw (vs string) option type=060, len=008: 31:32:33:34:35:36:37:38. As at the code very often assumes the option data type of a particular option this makes fused options invisible...

Some ideas for a fix:

• perform fusion before or during unpacking (how without requiring two passes?)
• use the definition from the option type/code (call unpack() ?)
• create a per option type (i.e. children of Option) fuse method