(non) translatable string splicing

I was surprised to see that this has been here for a few years (since
77517ba59) without complaints or inquiries from translators.

src/bin/pg_upgrade/option.c: check_required_directory(&old_cluster.bindir, "PGBINOLD", false,
src/bin/pg_upgrade/option.c- "-b", _("old cluster binaries reside"), false);
src/bin/pg_upgrade/option.c: check_required_directory(&new_cluster.bindir, "PGBINNEW", false,
src/bin/pg_upgrade/option.c- "-B", _("new cluster binaries reside"), true);
src/bin/pg_upgrade/option.c: check_required_directory(&old_cluster.pgdata, "PGDATAOLD", false,
src/bin/pg_upgrade/option.c- "-d", _("old cluster data resides"), false);
src/bin/pg_upgrade/option.c: check_required_directory(&new_cluster.pgdata, "PGDATANEW", false,
src/bin/pg_upgrade/option.c- "-D", _("new cluster data resides"), false);
src/bin/pg_upgrade/option.c: check_required_directory(&user_opts.socketdir, "PGSOCKETDIR", true,
src/bin/pg_upgrade/option.c- "-s", _("sockets will be created"), false);

src/bin/pg_upgrade/option.c: pg_fatal("You must identify the directory where the %s.\n"
src/bin/pg_upgrade/option.c- "Please use the %s command-line option or the %s environment variable.",
src/bin/pg_upgrade/option.c- description, cmdLineOption, envVarName);

Due to incomplete translation, that allows some pretty fancy output,
like:
| You must identify the directory where the residen los binarios del clúster antiguo.

That commit also does this a couple times:

+ _(" which is an index on \"%s.%s\""),

--
Justin