evolve: don't crash on singled out revisions
Before this patch, we were crashing on unsolvable revisions when using
evolve --rev. This patch removes the crash and prints a warning when we
encounter such revision.
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