See #61

See #61

See #61

See #61

Close #52

* Replace semaphores by pthread_mutexes
* Replace shmem nprocs by an array of pid_t
* Remove shmem_check_consistency function and add a consistency
    check based on stored pids
* Add an option to not delete Shared memory when calling shmem_finalize

Do not use LB_Barrier_QTY var, the number of processes that are in the barrier are all the ones that haver
done init with LB_Barrier=1

* API now receives a char ***environ
    - if NULL we use setenv
    - if !NULL, we must reallocate the custom environ to add our variable
* Shared Memory attachment now needs to look to an env. variable
    "LB_PREINIT" and use that value instead of the PID.
    (*) This won't be done in 1.3. To be fixed in 1.4
* Refactor PreRegister into PreInit

* Fix dlb_taskset to correctly finalize non-dlb aware applications
* The API can receive a boolean to determine whether to return the CPUs

This API is used by undetermined PM's that want to poll for new threads:
* int DLB_poll_new_threads(int *nthreads, dlb_cpu_set_t mask)

See #57

Basic error handling for DROM functions.