packaging: refactor "fedora29" target to a single more generic "fedora" target Fedora moves fast in version numbers, and often with Mercurial packaging being backwards compatible. Also, most people use the system package. There is thus much work and tech debt and little value in providing explicit built-in support for several versions. Thus, only aim for providing built-in support for latest Fedora version, and make it easy to update.

packaging: make dockerrpm fedora target more generic Fedora moves fast in version numbers, and often with Mercurial packaging being backwards compatible. Thus, only aim for providing built-in support for latest Fedora version, and make it easy to update. With this refactoring, 'dockerrpm fedora31' also works. 'dockerrpm fedora' will use the 'fedora:latest' Docker image.

packaging: use "python3" for fedora29 ... and as buildrpm default Change the buidrpm default. The CentOS targets explicitly use "python", and changing the default will only influence Fedora 29. A Python 3 package needs python3 dependencies, so pythonexe (and pythonver) is used for specifying dependencies. Other OS versions will keep using "python" as before ... or potentially change to explicit "python2". Fedora 29 packages can thus also still be built for Python 2 - just not in the docker image that is updated for Python 3.

packaging: use "--python python" for centos7 to avoid explicit "python2" This is a partial backout of 92a51a45d44c. We will need to be able to control whether package dependencies are python2 or python3. Generally (at least in recent Fedora), the package prefix match the name of the python executable ... but CentOS 7 doesn't use the python2 prefix in package name or alias for python-docutils yet, so just keep centos7 in the unversioned "python" world. Change the new (unused) buildrpm "--python3" option (introduced in a6dcac6454c1) to "--python python3" to get a more generic method for explicit control over whether we use python, python2 or python3.

packaging: fix docker-centos5 - use pythonexe and set to "python" as before Fix 92a51a45d44c .

packaging: move dockerrpm output directory creation to dockerrpm Avoid having to compute the directory in two places in different environments.

packaging: drop "support" for unsupported Fedora versions Fedora 31 has just been released, and Fedora 29 will be EOL in a month. Don't spend any time thinking about dead stuff.

mail: black wants to add this blank line I can't figure out how this got overlooked on previous runs, but here we are. It looks like the culprit change is already public?

hghave: verify we have a black that is new enough for our format We require what is currently the absolute latest black, so let's be paranoid.

contrib: fix up example fix configuration for our move to released black