This causes `upgrade-zulip-from-git`, as well as a no-option run of
`tools/build-release-tarball`, to produce a Zulip install running
Python 3, rather than Python 2. In particular this means that the
virtualenv we create, in which all application code runs, is Python 3.
One shebang line, on `zulip-ec2-configure-interfaces`, explicitly
keeps Python 2, and at least one external ops script, `wal-e`, also
still runs on Python 2. See discussion on the respective previous
commits that made those explicit. There may also be some other
third-party scripts we use, outside of this source tree and running
outside our virtualenv, that still run on Python 2.
In this commit, we are adding a new tool which can be used to
clear out the emoji cache. Cache cleanup is a good thing to in
general and as well helps keep travis cache small (meaning faster
builds).
Credits to @HarshitOnGitHub as well for suggesting the use of
emoji symlink.
Greg Price
Aditya Bansal