Move VerifySignature to main

src/main.h

@@ -164,6 +164,8 @@ bool SetBestChain(CBlockIndex* pindexNew);
 bool ConnectBestBlock();
 /** Create a new block index entry for a given block hash */
 CBlockIndex * InsertBlockIndex(uint256 hash);
+/** Verify a signature */
+bool VerifySignature(const CCoins& txFrom, const CTransaction& txTo, unsigned int nIn, unsigned int flags, int nHashType);