added variableSpending method.
added variableSpending method.

jchristian/cFIREsim-open,boknows/cFIREsim-open,jchristian/cFIREsim-open,treble37/cFIREsim-open,treble37/cFIREsim-open,boknows/cFIREsim-open,jchristian/cFIREsim-open,boknows/cFIREsim-open,treble37/cFIREsim-open