This patch reflects eventual allocation errors in a more specific way to
the caller of 'alloc_aligned', in particular out-of-metadata and
out-of-memory are considered as different conditions.
Related to issue #526.
This patch introduces the functions 'affinity' and 'num_cpus' to the CPU
session interface. The interface extension will allow the assignment of
individual threads to CPUs. At this point, it is just a stub with no
actual platform support.