Clean up warnings

* Use -Wall -Wextra -Wformat -Wformat-security -Wno-unused-parameters
* Remove xCXXFLAGS usage in makefile.unix
* Fix several recent and older sign-compare warnings

src/qt/transactionrecord.cpp

@@ -102,7 +102,7 @@ QList<TransactionRecord> TransactionRecord::decomposeTransaction(const CWallet *
                 //
                 int64 nTxFee = nDebit - wtx.GetValueOut();
 
-                for (int nOut = 0; nOut < wtx.vout.size(); nOut++)
+                for (unsigned int nOut = 0; nOut < wtx.vout.size(); nOut++)
                 {
                     const CTxOut& txout = wtx.vout[nOut];
                     TransactionRecord sub(hash, nTime);