postpone object build until break detected on join

[arnaudroger]

• have an intermediary builder that accumulate the data
• build on break
  would allow support for immutable collection, might also solve converge the csv mapping code.
  would could generate the builder using asm when asm enabled avoiding boxing.
  for all getter/setter we could just wrap the actual object and delegate? or would that be to complicated ?
  how to we make non join mapper not pay for that?