Unset environment variables that control message language, so that we
can compare some program output with expected strings. This is very
similar to what pg_regress does.
Creating the Unix-domain socket in the build directory can run into
name-length limitations. Therefore, create the socket file in the
default temporary directory of the operating system. Keep the temporary
data directory etc. in the build tree.
Peter Eisentraut
Bruce Momjian