use tr1::ref

[ichthyo]

At various places, I used boost::ref, i.e. the reference wrapper from boost. I wasn't aware that reference wrapper got part of std::tr1 (accessible through <tr1/functional>)

We should try to convert as much as possible to using the tr1 implementation. While initially, this was just an alias to boost, meanwhile the standard library ships its own implementation, and mixing both is apt to create subtle problems. (in the past, I already hit a similar situation with boost::function vs. tr1::function)