More nonce space added to the Bitcoin header (no hardfork)
This pull request contains the implementation of the BIP explained in
https://github.com/bcpki/nonce2bip/blob/master/nonce2.mediawiki

The patch shrinks the size of the nVersion field in each block to 2 bytes (UNIT16) and reserves 15 bits of the
original nVersion field for additional nonce space. This modification is not a hard-fork nor a soft-fork since
the protocol already allows using the nVersion as nonce.