Merge #1199: Clean up 4.0 compiler warnings

bccbec4 [Build] Clean up warnings (Cave Spectre)

Pull request description:

  ### Problem
  Compiler warnings when building off the v4.0 tag

  ### Root Cause
  Several different issues:
  ```
  init.cpp: In function ‘bool AppInit2()’:
  init.cpp:1442:13: warning: unused variable ‘nStart’ [-Wunused-variable]
       int64_t nStart = GetTimeMillis();
               ^~~~~~
  ```
  ```
  wallet/wallet.cpp: In member function ‘CAmount CWallet::GetCredit(const CTransaction&, const isminefilter&, bool) const’:
  wallet/wallet.cpp:5649:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
       for (int i = 0; i < tx.vout.size(); i++) {
                       ~~^~~~~~~~~~~~~~~~
  ```
  ```
  leveldb/util/logging.cc: In function ‘bool leveldb::ConsumeDecimalNumber(leveldb::Slice*, uint64_t*)’:
  leveldb/util/logging.cc:58:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             (v == kMaxUint64/10 && delta > kMaxUint64%10)) {
                                    ~~~~~~^~~~~~~~~~~~~~~
  ```
  ```
  qt/transactionrecord.cpp: In static member function ‘static QList<TransactionRecord> TransactionRecord::decomposeTransaction(const CWallet*, const CWalletTx&)’:
  qt/transactionrecord.cpp:221:57: warning: ‘*’ in boolean context, suggest ‘&&’ instead [-Wint-in-bool-context]
           if (fAllFromMeDenom && fAllToMeDenom && nFromMe * nToMe) {
                                                   ~~~~~~~~^~~~~~~
  ```
  ```
  In file included from qt/pivx/welcomecontentwidget.cpp:5:0:
  ./qt/pivx/welcomecontentwidget.h: In constructor ‘WelcomeContentWidget::WelcomeContentWidget (QWidget*)’:
  ./qt/pivx/welcomecontentwidget.h:44:18: warning: ‘WelcomeContentWidget::backButton’ will be initialized after  -Wreorder]
       QPushButton *backButton;
                    ^~~~~~~~~~
  ./qt/pivx/welcomecontentwidget.h:40:18: warning:   ‘QPushButton*

  WelcomeContentWidget::icConfirm1’ [-Wreorder]
       QPushButton *icConfirm1;
                    ^~~~~~~~~~
  qt/pivx/welcomecontentwidget.cpp:15:1: warning:   when initialized here [-Wreorder]
   WelcomeContentWidget::WelcomeContentWidget(QWidget *parent) :
   ^~~~~~~~~~~~~~~~~~~~
  ```

  ### Additional
  One other I didn't touch.
  ```
  qt/pivx/walletpassworddialog.cpp: In constructor ‘WalletPasswordDialog::WalletPasswordDialog(QWidget*)’:
  qt/pivx/walletpassworddialog.cpp:85:9: warning: unused variable ‘posXX’ [-Wunused-variable]
       int posXX = ui->lineEditPassword->width() - 30;
           ^~~~~
  ```
  Since I wasn't sure where exactly that dialog pops up to see if the posXX is actually needed and should have a `btnWatch->move()`; so i figured I would leave that to @furszy to take care of.

ACKs for top commit:
  random-zebra:
    utACK bccbec4
  Warrows:
    ACK bccbec4

Tree-SHA512: 02f783d5e5e5ad5327f5e38afbfc88e1acf22511713738144cb137bedbf1b78cc100754796f1a9f42386d116679cedca01e744f43249526691d64bb630e259f0

src/init.cpp

@@ -1439,7 +1439,6 @@ bool AppInit2()
     nCoinCacheSize = nTotalCache / 300; // coins in memory require around 300 bytes
 
     bool fLoaded = false;
-    int64_t nStart = GetTimeMillis();
     while (!fLoaded && !ShutdownRequested()) {
         bool fReset = fReindex;
         std::string strLoadError;

src/qt/pivx/welcomecontentwidget.cpp

@@ -15,11 +15,11 @@
 WelcomeContentWidget::WelcomeContentWidget(QWidget *parent) :
     QDialog(parent, Qt::FramelessWindowHint | Qt::WindowSystemMenuHint),
     ui(new Ui::WelcomeContentWidget),
-    backButton(new QPushButton()),
     icConfirm1(new QPushButton()),
     icConfirm2(new QPushButton()),
     icConfirm3(new QPushButton()),
     icConfirm4(new QPushButton()),
+    backButton(new QPushButton()),
     nextButton(new QPushButton())
 {
     ui->setupUi(this);

src/qt/transactionrecord.cpp

@@ -218,7 +218,7 @@ QList<TransactionRecord> TransactionRecord::decomposeTransaction(const CWallet*
             if (fAllToMe > mine) fAllToMe = mine;
         }
 
-        if (fAllFromMeDenom && fAllToMeDenom && nFromMe * nToMe) {
+        if (fAllFromMeDenom && fAllToMeDenom && ((nFromMe * nToMe) != 0)) {
             parts.append(TransactionRecord(hash, nTime, wtx.GetTotalSize(), TransactionRecord::ObfuscationDenominate, "", -nDebit, nCredit));
             parts.last().involvesWatchAddress = false; // maybe pass to TransactionRecord as constructor argument
         } else if (fAllFromMe && fAllToMe) {

src/wallet/wallet.cpp

@@ -5642,7 +5642,7 @@ CAmount CWallet::GetDebit(const CTransaction& tx, const isminefilter& filter) co
 CAmount CWallet::GetCredit(const CTransaction& tx, const isminefilter& filter, const bool fUnspent) const
 {
     CAmount nCredit = 0;
-    for (int i = 0; i < tx.vout.size(); i++) {
+    for (unsigned int i = 0; i < tx.vout.size(); i++) {
         if (fUnspent && IsSpent(tx.GetHash(), i)) continue;
         nCredit += GetCredit(tx.vout[i], filter);
     }