Make src/interfaces/libpq/test clean up after itself.

Tom Lane <tgl@sss.pgh.pa.us>

Commit: bde7d6d79464c453ddafd18c5f4e808c17c4f04f
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date: 2017-02-19T22:18:36Z
Releases: 9.6.3
Make src/interfaces/libpq/test clean up after itself.

It failed to remove a .o file during "make clean", and it lacked
a .gitignore file entirely.

Files