templater: provide loop counter as "index" keyword
This was originally written for JSON templating where we would have to be
careful to not add extra comma, but seems generally useful.
Inner loop started by % operator has its own counter.
# The test-repo is a live hg repository which may have evolution
# markers created, e.g. when a ~/.hgrc enabled evolution.
#
# Tests are run using a custom HGRCPATH, which do not
# enable evolution markers by default.
#
# If test-repo includes evolution markers, and we do not
# enable evolution markers, hg will occasionally complain
# when it notices them, which disrupts tests resulting in
# sporadic failures.
#
# Since we aren't performing any write operations on the
# test-repo, there's no harm in telling hg that we support
# evolution markers, which is what the following lines
# for the hgrc file do:
cat >> $HGRCPATH << EOF
[experimental]
evolution=createmarkers
EOF