This fixes ticket #85.

This works around a regression introduced in boost 1.48, relating to the
edge descriptors of reversed graphs.

See: https://svn.boost.org/trac/boost/ticket/6391

This fixes a bug where the PropertyMap.fa attribute would not be set if
filtering is disabled.

This fixes ticket #84

This also belongs to an upcoming commit.

This modification belongs to an upcoming commit.

This changes stlightly the information passed to the auxiliary functions
provided by the user, so that more arbitrary structures can be
constructed more easily.

The condensation_graph() function now returns a property map which
contains the community values themselves for each vertex.

This includes a spirit parser for the gml syntax, and a graph writer.

Additionaly, the general graph io code also been cleaned up.

This fixes ticket:73

Images are now converted to png a posteriori for html output, but are
used as pdf for latex.

This fixes a compile error with gcc 4.4 and boost in debian squeeze.

This fixes a bug in the "correlated" mode in random_rewire().

This implements a general "blockmodel" generation / rewiring algorithm,
using Gibbs acceptence / rejection sampling (a.k.a Metropolis-Hastings).

This also implements some optimizations in the rewiring code, which
makes it more efficient on filtered graphs.