obshash: properly cache obshash value
The code was buggy and only cached non-nullid/non-inherited value. This was
previous hidden because we were using a 'propertycache' to cache the value on
the range object. This fixes it and restore a lot of performance.
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