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

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

Commit: 4be0c2e4417920f27ba2886d2036a672f375fe34
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date: 2017-02-19T22:18:50Z
Releases: 9.3.17
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