[BioC] changes to RBGL

[Vincent Carey]

The Bioc 2.10 release image of RBGL has been modified in two significant ways
  1) boost (www.boost.org) C++ headers for graph algorithms are
now derived from boost 1.49
  2) RBGL C++ sources have been modified to compile cleanly with
g++ 4.7

This has necessitated (at least temporary) removal of boost-based
graph layout functions.  The loss seems unimportant given the availability
of Rgraphviz

There has been a minor change to the behavior of incremental.components

Similar changes are in place in the devel version.

Users and developers who encounter difficulties with these changes
should post details to the list.