Add rpath treatment to build system

Not quite tested yet on this particular project.
Works on UCL/purify.
Using script/cache files to pass arguments to external projects

This approach is safer than having cmake build a command-line. It means we can set variables that
have spaces in them...

It also means we can automatically pass a lot of variables to external projects that use cmake, via
the passon_variables function of the cookoff.
Missing cast in SWIG typemap when using c++11 in PyTrilinos
Merge branch 'rsdt/new_build' of github.com:bempp/bempp into rsdt/new_build