This change-set introduces parallelism on the committer. In particular, tx
generic validation (e.g. well-formedness, signature checks) and VSCC validation
are conducted in parallel for all transactions inside a block. This change-set
scales the *validation* throughput with number of cores on the machine that
runs the peer.

Change-Id: I80c03bd713a30f3db56627c7ae8fcf6fdd0d7891
Signed-off-by: Alessandro Sorniotti <ale.linux@sopit.net>