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.

This enables support for older versions of GCC (>=4.2), by falling back
to the boost tr1 implementation when the GCC version is less than 4.4.

The module dl has been deprecated, and has been replaced by ctypes. This
also fixes a problem where the dlopen() flags have different numbers in
different architectures.

Now the meaning of the bin edges given to the several histogram
functions are the same as in numpy/scipy. This means that the last bin
edge represents an upper bound on the last bin.

This fixes a bug in the motifs() code which generates a segfault for
certain subgraph signatures. This also fixes a potential problem for
multithreaded execution.