docs: add SPHINXBUILD make variable
This defaults to sphinx-build. The current use case is for the Evolve
Debian package build.
. $TESTDIR/testlib/common.sh
cat >> $HGRCPATH <<EOF
[ui]
interactive = true
[phases]
publish=False
[extensions]
evolve =
[experimental]
evolution.effect-flags = yes
EOF
sync() {
hg pull -R $TESTTMP/server . -q
}