Merged first batch of 1.51 changes for Boost.Graph and Boost.PropertyMap

svn path=/branches/release/boost/property_map/; revision=79189
Second batch of Boost.Graph and Boost.PropertyMap changes for 1.51

svn path=/branches/release/boost/property_map/; revision=79191
Merged more changes (bug fixes, especially hopefully fixing the VC++ test failure) from trunk

svn path=/branches/release/boost/property_map/; revision=79390