global variables prev_shmem_request_hook and prev_shmem_startup_hook missing prefix pglogical

[okbob]

I had to solve an collision of names between plpgsql_check and pglogical. In both projects was used an public variables prev_shmem_request_hook and prev_shmem_startup_hook - see https://github.com/okbob/plpgsql_check/issues/152