evolve: make uncommit respect allowunsable
Before this patch, the uncommit command was performing the same way regardless
of the value of experimental.evolution.
With this patch if the configuration does not allow unstability, uncommit won't
create instability.
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