Make lsn_reset ("detach databases") optional and off by default.

Add an option -detachdb (and entry in OptionDialog), without which no
lsn_reset is called on addr.dat and blkindex.dat. That means these
files cannot be moved to a new environment, but shutdown can be
significantly faster. The wallet file is always lsn_reset'ed.

-detachdb corresponds to the old behaviour, though it is off by
default now to speed up shutdowns.

src/qt/optionsdialog.cpp

@@ -38,6 +38,7 @@ private:
     QCheckBox *minimize_on_close;
 #endif
     QCheckBox *connect_socks4;
+    QCheckBox *detach_database;
     QLineEdit *proxy_ip;
     QLineEdit *proxy_port;
     BitcoinAmountField *fee_edit;
@@ -229,6 +230,10 @@ MainOptionsPage::MainOptionsPage(QWidget *parent):
 
     layout->addLayout(fee_hbox);
 
+    detach_database = new QCheckBox(tr("Detach databases at shutdown"));
+    detach_database->setToolTip(tr("Detach block and address databases at shutdown. This means they can be moved to another data directory, but it slows down shutdown. The wallet is always detached."));
+    layout->addWidget(detach_database);
+
     layout->addStretch(1); // Extra space at bottom
 
     setLayout(layout);
@@ -256,6 +261,7 @@ void MainOptionsPage::setMapper(MonitoredDataMapper *mapper)
     mapper->addMapping(proxy_ip, OptionsModel::ProxyIP);
     mapper->addMapping(proxy_port, OptionsModel::ProxyPort);
     mapper->addMapping(fee_edit, OptionsModel::Fee);
+    mapper->addMapping(detach_database, OptionsModel::DetachDatabases);
 }
 
 DisplayOptionsPage::DisplayOptionsPage(QWidget *parent):

src/qt/optionsmodel.cpp

@@ -28,6 +28,8 @@ void OptionsModel::Init()
         SoftSetBoolArg("-upnp", settings.value("fUseUPnP").toBool());
     if (settings.contains("addrProxy") && settings.value("fUseProxy").toBool())
         SoftSetArg("-proxy", settings.value("addrProxy").toString().toStdString());
+    if (settings.contains("detachDB"))
+        SoftSetBoolArg("-detachdb", settings.value("detachDB").toBool());
 }
 
 bool OptionsModel::Upgrade()
@@ -121,6 +123,8 @@ QVariant OptionsModel::data(const QModelIndex & index, int role) const
             return QVariant(nDisplayUnit);
         case DisplayAddresses:
             return QVariant(bDisplayAddresses);
+        case DetachDatabases:
+            return QVariant(fDetachDB);
         default:
             return QVariant();
         }
@@ -204,6 +208,11 @@ bool OptionsModel::setData(const QModelIndex & index, const QVariant & value, in
             settings.setValue("bDisplayAddresses", bDisplayAddresses);
             }
             break;
+        case DetachDatabases: {
+            fDetachDB = value.toBool();
+            settings.setValue("detachDB", fDetachDB);
+            }
+            break;
         default:
             break;
         }

src/qt/optionsmodel.h

@@ -26,7 +26,8 @@ public:
         Fee, // qint64
         DisplayUnit, // BitcoinUnits::Unit
         DisplayAddresses, // bool
-        OptionIDRowCount
+        DetachDatabases, // bool
+        OptionIDRowCount,
     };
 
     void Init();