evolve: fix error in builddependencies When MultipleSuccessorsError was raised, we were still running the code below to add the dependency if succ was not None from a previous iteration. This bug was harmless because dependencies and rdependencies are sets but it makes the code clearer this way.

all: tutorials/tutorial.rst static/logo-evolve.ico
	sphinx-build . ../html/

tutorials/tutorial.rst: tutorials/tutorial.t
	python test2rst.py tutorials/

static/logo-evolve.ico: static/logo-evolve.svg
	convert -resize 36x36 static/logo-evolve.svg static/logo-evolve.ico