Hi,
When I use the 'pqmq' recently, I found some issues, just fix them.
Allow the param 'dsm_segment *seg' to be NULL in function
'pq_redirect_to_shm_mq'. As sometimes the shm_mq is created
in shared memory instead of DSM.
Add function 'pq_leave_shm_mq' to allow the process to go
back to the previous pq environment.
