Tidy snippets: Reorder variables to e.g. list legacy before modern, and cdbs_curpkg-resolved later.
Tidy snippets: wrap+strip wide lines, and strip trailing whitespace.
Introduce new expansion variables cdbs_uc cdbs_lc.
Fix python-distutils.mk and python-sugar.mk to use unversioned runtime for default flavor (see bug#377964).
Modernize python-distutils.mk installdir handling (since supported even in oldstable now): Use --install-layout=deb (and drop --prefix=/usr) by default, and use --install-lib option (not --install-purelib/--install-platlib, and only when DEB_PYTHON_DISTUTILS_INSTALLDIR_SKEL is set).  Deprecate cdbs_expand_python_distutils_installdir, and have it provide .../dist-packages dir (not .../site-packages) by default to try cope with packages relying on it for non-skel use. Closes: bug#565973. Thanks to Matthias Klose and Piotr Ożarowski.
Fix error message to talk about multiple python implementations (not packaging systems nor too specific ones).
Tidy excess whitespace.
Tidy python-vars.mk: Add/improve comments.
Introduce new variables DEB_CONFIGURE_SCRIPT_ENV_PYTHON cdbs_make_curpythonruntime cdbs_autotools_configure_env, for custom use of autotools and to allow early override only of python env.
Rename cdbs_python_pysupport → cdbs_pythonsystem_pysupport. Drop the former without deprecation (unused outside cdbs).

Dropped variable verified against <http://codesearch.debian.net>.
Rename cdbs_python_pycentral → cdbs_pythonsystem_pycentral. Drop the former without deprecation (unused outside cdbs).

Dropped variable verified against <http://codesearch.debian.net>.
Rename cdbs_python2 → cdbs_pythonsystem_python2. Drop the former without deprecation (unused outside cdbs).

Dropped variable verified against <http://codesearch.debian.net>).
Rename cdbs_python3 → cdbs_pythonsystem_python3. Drop the former without deprecation (unused outside cdbs).

Dropped variable verified against <http://codesearch.debian.net>.
Refactor python snippets: Expand implementations from lists.
Drop per-flavor variables python_*_packages (replace with private variables) without deprecation (unused outside cdbs).

Verified against <http://codesearch.debian.net>.
Drop unused make targets python-install-py python-install-% python-clean-% python-build-stamp-%.

Verified against <http://codesearch.debian.net>.
Drop variable cdbs_python_stem (replace with private variable) without deprecation (unused outside cdbs).

Verified against <http://codesearch.debian.net>.
Refactor python snippets: Handle flavors (not versions). Introduce new variables cdbs_python_flavors cdbs_curpython, and per-implementation variables cdbs_$python_mainflavor. Drop unused variables cdbs_pythonsystem_python3 cdbs_python_stem cdbs_python_first_supported_version cdbs_python3_first_supported_version cdbs_python_nondefault_version cdbs_python3_nondefault_version cdbs_python_primary_version cdbs_python3_primary_version cdbs_curpythonbuildversions. Deprecate variables cdbs_curpythonstem cdbs_python_current_binary cdbs_python3_current_binary cdbs_python_current_version cdbs_python3_current_version cdbs_python_supported_versions cdbs_python3_supported_versions cdbs_python_build_versions.

Dropped variables verified against <http://codesearch.debian.net>.
Rename cdbs_python2_builddeps → cdbs_python_builddeps_python2. Drop the former without deprecation (unused outside cdbs).

Dropped variable verified against <http://codesearch.debian.net>.
Rename cdbs_python3_builddeps → cdbs_python_builddeps_python3. Drop the former without deprecation (unused outside cdbs).

Dropped variable verified againt <http://codesearch.debian.net>.