Per report from Caleb Cushing (xenoterracide).
Right now it's just a stub that does a very simple test. More tests can be added later.
This is necessary both for supporting versions of PostgreSQL that don't have EXTENSION support, and for the test infrastructure to work. The .sql.in file is used both to create the current extension version .sql file and to generate a .sql file. However, the .sql.in file and the generated .sql file need to live in the top level directory, or the MODULE_PATHNAME is not replaced properly.
Restructure the directories and add control files so that it will conform to the expectations of CREATE EXTENSION as well as PGXN.
All contrib modules have this line, and it being there make it easier to treat the temporal module like other extensions in terms of changing that line for installing it into a different schema.
This makes it easier to unpack a temporal release into the `contrib` directory of an unpacked PostgreSQL source tarball and to install it like any other contrib module.