Manage classes of search paths in labeled containers. This removes the
need to have a seperate member variable for each type of search path, but
also allows path types to be grouped togethor in various different ways
and manipulated as subsets of the full set of search paths.
The functions for adding the various different types of paths have been
factored out into a new class, cmSearchPath. It is to be used as a helper
container class for the various find_* commands.
Stephen Kelly
Gregor Jasny
Chuck Atkins
Brad King