add constant for shared (GUI/core) -par settings

- introduce DEFAULT_SCRIPTCHECK_THREADS in main.h
- only show values from -"MAX_HW_THREADS" up to 16 for -par, as it
  makes no sense to try to leave more "cores free" than the system
  supports anyway
- use the new constant in optionsdialog and remove defaults from
  .ui file

src/qt/forms/optionsdialog.ui

@@ -98,13 +98,7 @@
          <item>
           <widget class="QSpinBox" name="threadsScriptVerif">
            <property name="toolTip">
-            <string>Set the number of script verification threads (up to 16, 0 = auto, &lt;0 = leave that many cores free, default: 0)</string>
-           </property>
-           <property name="minimum">
-            <number>-16</number>
-           </property>
-           <property name="maximum">
-            <number>16</number>
+            <string>(0 = auto, &lt;0 = leave that many cores free)</string>
            </property>
           </widget>
          </item>

src/qt/optionsdialog.cpp

@@ -14,7 +14,7 @@
 #include "monitoreddatamapper.h"
 #include "optionsmodel.h"
 
-#include "main.h" // for CTransaction::nMinTxFee
+#include "main.h" // for CTransaction::nMinTxFee and MAX_SCRIPTCHECK_THREADS
 #include "netbase.h"
 #include "txdb.h" // for -dbcache defaults
 
@@ -37,6 +37,8 @@ OptionsDialog::OptionsDialog(QWidget *parent) :
     /* Main elements init */
     ui->databaseCache->setMinimum(nMinDbCache);
     ui->databaseCache->setMaximum(nMaxDbCache);
+    ui->threadsScriptVerif->setMinimum(-(int)boost::thread::hardware_concurrency());
+    ui->threadsScriptVerif->setMaximum(MAX_SCRIPTCHECK_THREADS);
 
     /* Network elements init */
 #ifndef USE_UPNP

src/qt/optionsmodel.cpp

@@ -76,6 +76,17 @@ void OptionsModel::Init()
     // by command-line and show this in the UI.
 
     // Main
+    if (!settings.contains("nDatabaseCache"))
+        settings.setValue("nDatabaseCache", (qint64)nDefaultDbCache);
+    if (!SoftSetArg("-dbcache", settings.value("nDatabaseCache").toString().toStdString()))
+        addOverriddenOption("-dbcache");
+
+    if (!settings.contains("nThreadsScriptVerif"))
+        settings.setValue("nThreadsScriptVerif", DEFAULT_SCRIPTCHECK_THREADS);
+    if (!SoftSetArg("-par", settings.value("nThreadsScriptVerif").toString().toStdString()))
+        addOverriddenOption("-par");
+
+    // Wallet
 #ifdef ENABLE_WALLET
     if (!settings.contains("nTransactionFee"))
         settings.setValue("nTransactionFee", 0);
@@ -89,16 +100,6 @@ void OptionsModel::Init()
         addOverriddenOption("-spendzeroconfchange");
 #endif
 
-    if (!settings.contains("nDatabaseCache"))
-        settings.setValue("nDatabaseCache", (qint64)nDefaultDbCache);
-    if (!SoftSetArg("-dbcache", settings.value("nDatabaseCache").toString().toStdString()))
-        addOverriddenOption("-dbcache");
-
-    if (!settings.contains("nThreadsScriptVerif"))
-        settings.setValue("nThreadsScriptVerif", 0);
-    if (!SoftSetArg("-par", settings.value("nThreadsScriptVerif").toString().toStdString()))
-        addOverriddenOption("-par");
-
     // Network
     if (!settings.contains("fUseUPnP"))
 #ifdef USE_UPNP