This implements indirect array access to property maps with vector
values.

This changes the way search visitors are wrapped, such that the original
class remains unmodified. With the previous code, the original classes
would be repeatedly modified, adding unnecessary overhead, and even
possibly causing the number of nested calls to exceed the maximum
threshold.

This also improves some of the existing shuffling strategies with a fast
alias sampling. The parameter names of the random_graph() and
random_rewire() functions have been made more consistent.

The graphml reader no longer builds a list of edges/vertices during
parsing, whenever the graph uses canonical names.

These are redundant functions which can be trivially implemented as
loops.

This fixes ticket #131, and includes a 'fast' O(k) option, which
changes the vertex index ordering.

This is done by default in depth_first_search() in BGL, so we switch to
depth_first_visit().