* Initial work on flag trapping using functions called <flag>_handler and default_flag_handler
* Update packages so they do not obliterate flags
* Added append to EnvironmentModifications class
* changed EnvironmentModifications to have append_flags method
* changed flag_val to be a tuple
* Increased test coverage
* added documentation of flag handling
* Change path to CMakeLists.txt to be relative to root, not pwd
* Changes requested during code review
* Revert back to old naming of root_cmakelists_dir
* Make relative directory more clear in docs
* Revert change causing build_type AttributeError
* Fix forgotten abs_path var
* Update CLHEP with new relative path
* Update more packages with new root_cmakelists_dir syntax
