graph_draw() won't work if gv is not available, and just a warning is
printed... This makes graph_tool.all work when gv is not available.

Fix bad_any_cast bug when passing a weight property.

This fully documents the centrality module.

The function directed() no longer exists, is_directed() should be used
instead.

The _max_edge_index variable was not set when reading a graph, which
caused memory corruption when deleting and adding edges.

Now all filters are stashed by default. In order to override this, the
parameter all=False needs to be passed, and the individual filters need
to be specified.

This also doesn't build a parallel vertex list if motifs aren't being
sampled.

This includes the function motif_significance() into the clustering
module.

This changes the meaning of the all_selectors type, which includes all
property types, and creates a scalar_selectors type, which includes only
the scalar types.

Conflicts:
	acinclude.m4
	configure.in
	src/graph-tool
	src/graph/Makefile.am
	src/graph/correlations/graph_assortativity.hh
	src/graph/graph.cc
	src/graph/graph_betweenness.cc
	src/graph_tool/__init__.py

This ensures that vector types also don't suffer from data loss due to
representation change.

Individual filters can be stashed and popped by passing keyword
arguments to the respective functions. Additionally the filter state can
be obtained and set directly, with the get_filter_state() and
set_filter_state() functions.

This finally fixes in the bug addressed by commit 309ddbbd, where
parallel edges could be erroneously created. In fact, the bug was more
serious: The source and target edge lists always pointed to the same
list (in the uncorrelated case, but could occasionally happen for the
correlated case also) which got shuffled during iteration. Since the
shuffling of one list interfered with the shuffling of the other, some
combinations of source and target edges could simply never be
considered... This commit forces both lists to always be independent.

Thins changes the graph filtering code slightly to wrap graph types with
GraphWrap, which automatically updates the edge index list when edges
are removed and added to the graph.

This also changes how graphs are passed to algorithms, which is now by
reference instead of pointer. (hence this touches lots of code, but
changes are trivial)

This was not working due to filtering semantics modifications.

This implements an efficient motif counting algorithm.

Edge index housekeeping was not preserved during copy.

This fixes bug where boost overlay files were not being used, when not
compiling from source dir.

The edge index housekeeping was not performed on edges which were
deleted due to vertex removal.

This provides a more convenient way of deleting vertices or edges
according to a simple criterion.

Make sure libtool is properly modified, by doing it last in
configure.ac.

Add support for v.{out|in}_neighbours(), for direct iteration over the
neighbours, as well as v.all_edges() and v.all_neighbours(). This also
properly exports the Vertex and Edge classes, with docstrings.

This adds the centrality module, which supports betweenness, eigentrust,
pagerank and absolute trust.

This makes the naming more sensible.

It now does not implies automatically "always_directed".

In some circumstances, the test for parallel edges would fail to detect
one, if it involved another "new" edge and one of the current ones being
rewired.

This commit also removes the requirement that edge indexes be continuous
in the range [0, num_edges(g)), which is not in general the case.

The seed option is now correctly interpreted.