Fix bin/Makefile to pass regression tests sucessfully.
Fix bin/Makefile to pass regression tests sucessfully.

Without this fix, load_bin test fails because pg_bulkload sets
ENCODING with client_encoding when INPUT = stdin.

bwtakacy/pg_bulkload,bwtakacy/prev_pg_bulkload_repo,bwtakacy/pg_bulkload,ooyamams/pg_bulkload,bwtakacy/pg_bulkload,bwtakacy/prev_pg_bulkload_repo,bwtakacy/prev_pg_bulkload_repo,ooyamams/pg_bulkload,ooyamams/pg_bulkload