Move Parse{Hash|Hex} to be usable by all RPC code
Add RPC call decodescript
Make validateaddress provide redeemScript
Merge pull request #2830 from petertodd/p2sh-rpc

P2SH related RPC improvements
Squashed 'src/secp256k1/' content from commit 350ade2

git-subtree-dir: src/secp256k1
git-subtree-split: 350ade2ab4bccc3f7f846da28734f3546c09d8a5
Merge commit 'da0599324f809c9780560e7e120bd2fd6e415f73' as 'src/secp256k1'
Support for libsecp256k1
gitian support for secp256k1 linux builds