16377: back up env to SAGE_ROOT/.orig-env
Merge branch 'u/rws/back_up_environment_on_sage_startup' of trac.sagemath.org:sage into pb-2

* 'u/rws/back_up_environment_on_sage_startup' of trac.sagemath.org:sage:
  16377: back up env to SAGE_ROOT/.orig-env