* lib/calculus/fourier.gel: fix cosine series and fix argument
	  checking on the fourier function creation

	* src/geniustests.txt, src/testfourier.gel: add tests for the
	  fourier functions

	* src/graphing.c: the create plot and plot dialogs are stupid as
	  dialogs because of the way metacity handles dialogs (annoyingly
	  as "keep above parent") so set the hint to normal.