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See merge request !6

Change syntax for xml entities

See merge request !7

	* lib/number_theory/primes.gel: Update to newest data from GIMPS

A change for libxml2 tightened what syntax is allowed in entities:
libxml2@01411e7c

This makes the po/update-po.sh script error out at the itstool step.

This commit escapes the ampersand character as well as in the libxml2
example above, and makes the script work again for me.

	* src/graphing.c: fix off by one in the computing of the graphing
	  subintervals for surface plots

	* examples/zoom-differentiability.gel: wait for a moment at the
	  start, and a slightly different nondifferentiable function

	* src/graphing.c: improve slightly again efficiency, and make
	  rotation by holding down a key work better.

	* src/graphing.c: surface plots got recomputed twice, so only compute
	  once and setup in the same way as when plotting data, except
	  recomputing the data on zoom.

	* src/gnome-genius.c: Fix unsetting the stop button on script end,
	  fix current program marking.

	* src/graphing.c: Fix a couple of possible crashes when resetting
	  variable names.

	* graphing.c: improve slightly the frozenness of 3d plots, and enable
	  the stop button on the graph window the whole time a script is running.

	* examples/zoom-differentiability.gel: Example of zooming into a
	  differentiable and a nondifferentiable function of two variables

	* src/gnome-genius.c: allow setting editor color scheme in the
	  gui settings

	* src/gnome-genius.c: Make icons optional (ifdef'ed out), it actually
	  seems to me to look better without.