Python: fix dendrogram printing on Python 3.x, thanks to Jeremy Kun
Python: fixed Dendrogram.optimal_count getter
fixed igraph_closeness example in tutorial, closes #626
allow errors from igraph_i_lad_createGraph to propagate upwards, thanks to
Vassilis Pandis
Fixed boolean attributes in C, #641

igraph_copy did not copy the boolean attributes, thanks
to Disa for finding this.
Merge remote-tracking branch 'igraph/develop' into develop