This also keeps compatibility with earlier versions of boost.

This fixes ticket 61:

http://projects.skewed.de/graph-tool/ticket/61

This module contains several search algorithms and a visitor interface.

Now an explicit conversion to a compatible python type is attempted if
the value being set in a property map cannot be converted directly to a
C++ type.

This also fixes a bug with vector-valued property maps.

Now, whenever GraphWrap is being used, the property maps are always
in "checked" mode.

The arrays returned by PropertyMap.get_array() are now PropertyArray
instances, which keep track of the PropertyMap data, and are able to
detect when it changes, and raise a ValueError exception. As such, it
becomes impossible to read or write to non-allocated memory if an array
becomes invalid.

This fixes a bug where histograms constructed in parallel would
sometimes fail to count some samples.

This avoid a namespace clash when using run_action.inline().

These functions/properties provide more information and control about
edge indexing, which might be useful.

The reserved size for the array was set to g.num_edges(), but it should
be set to the maximum edge index + 1, since some edges might have been
deleted.