Function strstr cannot be used to remove tokens since it
may remove options that contain a substring of other option

Fix #89

- rebind also from the beginning
- preserve previous binding if possible
- do no set dirty flag if no thread needs rebinding

Optimize shmem functions that iterate all CPUs looking for
available CPUs by comparing the timestamps of the last borrow
and the last lent.

Kernel functions are now shared between APIs and DLB_kernel_sp
can be removed.

Now each specific shmem_print_info function opens a temporary
fd to the shared memory if necessary

* DLB_kernel does no longer manages specific lewi arrays
* cpus_priority_array is encapsulated into an opaque lewi_info pointer
* Declare a specific lewi_info_t for LeWI_mask particular variables
* Only Init/Finalize functions get a non-const spd