[libcalamares] Reduce warnings in KDAB code

- Use nullptr and suitable include guards

src/libcalamares/kdsingleapplicationguard/kdsingleapplicationguard.h

@@ -1,5 +1,5 @@
-#ifndef __KDTOOLSCORE_KDSINGLEAPPLICATIONGUARD_H__
-#define __KDTOOLSCORE_KDSINGLEAPPLICATIONGUARD_H__
+#ifndef KDTOOLSCORE_KDSINGLEAPPLICATIONGUARD_H
+#define KDTOOLSCORE_KDSINGLEAPPLICATIONGUARD_H
 
 #include <QtCore/QObject>
 
@@ -31,9 +31,9 @@ public:
         AutoKillOtherInstances = 1
     };
 
-    explicit KDSingleApplicationGuard( QObject * parent=0 );
-    explicit KDSingleApplicationGuard( Policy policy, QObject * parent=0 );
-    explicit KDSingleApplicationGuard( const QStringList & arguments, QObject * parent=0 );
+    explicit KDSingleApplicationGuard( QObject * parent=nullptr );
+    explicit KDSingleApplicationGuard( Policy policy, QObject * parent=nullptr );
+    explicit KDSingleApplicationGuard( const QStringList & arguments, QObject * parent=nullptr );
     explicit KDSingleApplicationGuard( const QStringList & arguments, Policy policy, QObject * parent=0 );
     ~KDSingleApplicationGuard();
 
@@ -138,4 +138,4 @@ QT_END_NAMESPACE
 
 #endif // QT_NO_SHAREDMEMORY
 
-#endif /* __KDTOOLSCORE_KDSINGLEAPPLICATIONGUARD_H__ */
+#endif /* KDTOOLSCORE_KDSINGLEAPPLICATIONGUARD_H */

src/libcalamares/kdsingleapplicationguard/kdtoolsglobal.h

@@ -1,5 +1,5 @@
-#ifndef __KDTOOLS_KDTOOLSGLOBAL_H__
-#define __KDTOOLS_KDTOOLSGLOBAL_H__
+#ifndef KDTOOLS_KDTOOLSGLOBAL_H
+#define KDTOOLS_KDTOOLSGLOBAL_H
 
 #include <QtCore/QtGlobal>
 
@@ -110,5 +110,5 @@ private:                                                                \
     void init(bool)
 
 
-#endif /* __KDTOOLS_KDTOOLSGLOBAL_H__ */
+#endif /* KDTOOLS_KDTOOLSGLOBAL_H */
 

src/libcalamares/kdsingleapplicationguard/pimpl_ptr.h

@@ -1,5 +1,5 @@
-#ifndef __KDTOOLSCORE__PIMPL_PTR_H__
-#define __KDTOOLSCORE__PIMPL_PTR_H__
+#ifndef KDTOOLSCORE__PIMPL_PTR_H
+#define KDTOOLSCORE__PIMPL_PTR_H
 
 #include "kdtoolsglobal.h"
 
@@ -14,7 +14,7 @@ namespace kdtools {
     public:
         pimpl_ptr() : d( new T ) {}
         explicit pimpl_ptr( T * t ) : d( t ) {}
-        ~pimpl_ptr() { delete d; d = 0; }
+        ~pimpl_ptr() { delete d; d = nullptr; }
 
         T * get() { return d; }
         const T * get() const { return d; }
@@ -40,5 +40,5 @@ namespace kdtools {
 } // namespace kdtools
 #endif
 
-#endif /* __KDTOOLSCORE__PIMPL_PTR_H__ */
+#endif /* KDTOOLSCORE__PIMPL_PTR_H */