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

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

Commit: 045462960f7c30608ebd7085697f1402d1e1500c
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date: 2017-02-19T22:18:46Z
Releases: 9.4.12
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