. Add indirect dependency on roscpp-core in depend.mk

. Add a bunch of %-config.cmake in SYSTEM_SEARCH

Make sure to pass all variables defining the proper python version as found by
robotpkg, otherwise ros CMakeFiles may happily find python-3.2 and use it
instead of python<3, although this does not work in the end (at least ros-rx
does this and breaks on F17).

This is done in the common ros Makefile as this affects all packages.

- Add missing dependency on log4cxx + boost headers for rosout
- Fix build with boost>=1.50

The ros_comm stack contains the ROS middleware/communications packages. This
packages are collectively known as the ROS "Graph" layer. They provide
implementations and tools for topics, nodes, services, and parameters. This
includes the supported ROS client libraries: roscpp, rospy, and roslisp.