Disable internal bounds checking in property maps
This includes a new vector property map type (fast_vector_property_map) which has optional disabling of bounds checking, through its associate map type (unchecked_fast_vector_property_map). This should improve performance on algorithms which depend on tight loops which access property maps. Bounds checking is only disabled locally just before the algorithms run, and proper care is taken for bounds checking _beforehand_. The property maps exposed to python still have internal bounds checking.