Changed buildfile so that it no longer duplicates environment classpath values. New build targets should depend on create-base-export-file to initiate the export file.
Removed execute permissions of .export-rospath and rexos-build.sh. These files should be called using source to make sure the user's environment is changed, rather than that of a subshell.
Added some comments to the rexos-build script and added a -c flag to clean rather than build.