CONFIG: adjust make scripts for darwin

- handling of dead links (find -L -delete unsupported)

- remove ignore case flag on 's/../../i' used in have_scotch script.
  It is unneeded and not tolerated by Darwin's sed.

- avoid embedded comments in EXE_INC (Make/options files), which do
  not work well with the OSX LLVM cpp.
  It strips out the comments but also removes the continuation char.

STYLE: adjust notes about paraview library locations