[py3] Avoid setting attribute on Element instance in wdoc view This change is needed to make "wdoc" view work on Python 3. Indeed, before this patch, we used to set a "parent" attribute on Element instances, which is not permitted since Python 3.3 as xml.etree.ElementTree uses the C implementation by default. To get rid of this "parent" attribute, we rework the XML nodes processing logic to return and retrieve a node along with its parent in several place of the code. Namely, build_toc_index() now accepts the "parent" value for "node" and inserts it in the "index" dict (thus avoid `node.parent = <value>`). Respectively, every query to the "index" dict is updated to also retrieve the "parent" (thus avoiding `<value> = node.parent`). Later in InlineHelpView class, the "index" dict is bound to "tocindex" attribute so we adjust how it is queried in respective methods. Tests cubicweb/web/test/unittest_views_wdoc.py now pass on Python 3.

#!/usr/bin/make -f
# Sample debian/rules that uses debhelper.
# GNU copyright 1997 to 1999 by Joey Hess.

# Uncomment this to turn on verbose mode.
# export DH_VERBOSE=1

export PYBUILD_NAME=cubicweb
export PYBUILD_DISABLE_python2=test

%:
	dh $@ --with python2,sphinxdoc --buildsystem=pybuild

override_dh_auto_build: export http_proxy=127.0.0.1:9
override_dh_auto_build: export https_proxy=127.0.0.1:9
override_dh_auto_build:
	dh_auto_build
ifeq (,$(findstring nodocs, $(DEB_BUILD_OPTIONS)))
	PYTHONPATH=. sphinx-build -N -bhtml doc/ debian/cubicweb-doc/html
endif

override_dh_auto_install:
	dh_auto_install
	mv debian/python-${PYBUILD_NAME}/usr/bin/cubicweb-ctl \
		debian/cubicweb-ctl/usr/bin/cubicweb-ctl

override_dh_installchangelogs:
	dh_installchangelogs -Xdoc/changes