evolve: search divergence within all precursors
Before this patches we looking for divergence base in immediate successors only.
This was a bug leading the divergence base to be reported missing more than it
should.
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