This fixes issue #624

This improves performance of the Python API.

This fixes a problem with stack corruption in graph_draw().

It now accepts edge descriptors from all graph views and invalidates
them after removal.

This fixes issue #318

This preserves the synchrony between global states and the iteration
sequence.

This introduces support for returning a generator in
subgraph_isomorphism(), so that all matches do not need to be kept on
memory simultaneously.

This fixes issue #255.

This ensures that the array is always of the correct size.

This fixes a bug where equal edge descriptors would be considered
unequal. Additionally, now Vertex and Edges can be ordered (via >, <,
>=, <=).

The new format fully supports all property map types present in
graph-tool and should be much faster and produce smaller files than the
other text-based formats.

Dumping boost::adjacency_list<> improves memory usage by a factor of
two, and also slightly improves performance in some cases.

This fixes the edge invalidation check, when either the source of the
target vertex is removed.