[Tree-hh] tree.hh version 2.60 released

[Kasper Peeters]

Dear all,

I have just released tree.hh version 2.60. This update mainly eliminates
a number of bugs related to fixed_depth iterators.

Code and documentation are, as usual, available from

    http://www.aei.mpg.de/~peekas/tree/

Best,
Kasper