Less confused about absolute/relative/symbolic pathnames now.
Fixes Linux global build.
Fix the global build on linux.
Prevent double inclusion of CommonPaths.h as pointed out by Glenn.
Some pathnames are used both by SCons and cpp which can be a bit tricky.
Should revisit and make the distinction more explicit.
Put the Data and Sys directories under Resources in the OS X app bundle.
Construct config.h (now lower-case to avoid confusion with other Config.h
instances in the tree) in the root. One tiny step towards a read-only
and cross-buildable source tree.
Some minor bits of non-Linux Unix portability.