Pre-rebase snapshot of PR #6 (moe/mpp-in-process-cleanup) tip; this i…

…s the exact commit pinned in pg_search/Cargo.toml.

Pre-rebase snapshot of PR #4 (moe/mpp-skip-grpc-on-unaddressed) tip; …

…preserves the commit ID pg_search depends on indirectly via PR #6 / d3cd758.