compat: make obshistory._getdifflines compatible with mercurial 4.1
On Mercurial version 4.1 and lower, patch.diff seems to returns an empty list
when there is no change. Mercurial 4.2 returns None so we add a if for this
case.
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