This adds support for using PGroonga to back the Zulip full-text
search feature. Because built-in PostgreSQL full text search doesn't
support languages that don't put space between terms such as Japanese,
Chinese and so on. PGroonga supports all languages including Japanese
and Chinese.
Developers will need to re-provision when rebasing past this patch for
the tests to pass, since provision is what installs the PGroonga
package and extension.
PGroonga is enabled by default in development but not in production;
the hope is that after the PGroonga support is tested further, we can
enable it by default.
Fixes#615.
[docs and tests tweaked by tabbott]
When running ./tools/test-backend, the script to generate
fixtures, ./tools/setup/generate-fixtures, looks for a file
called migration-status to determine whether it can short
circuit doing database migrations. This file got moved as
part of the effort to put files in "var," but the existence
check was still looking for that file in its old location.
Factor out the code in tools/provision.py which installs a python2
and python3 venv into a module (tools/setup/setup_venvs.py) which
can also be used as a script.