QEasingCurve: implement copy assignment operator inline

Implement the copy-assignment operator inline, using the
copy-swap idiom. This makes assignment strongly exception
safe, but also simplifies maintainence, because op= is
formulated in terms of the copy constructor now.

Change-Id: I803c9100a520d659b685992237cb76fd114222c8
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qeasingcurve.cpp

@@ -1100,22 +1100,9 @@ QEasingCurve::~QEasingCurve()
 }
 
 /*!
+    \fn QEasingCurve &QEasingCurve::operator=(const QEasingCurve &other)
     Copy \a other.
  */
-QEasingCurve &QEasingCurve::operator=(const QEasingCurve &other)
-{
-    // ### non-atomic, requires malloc on shallow copy
-    if (d_ptr->config) {
-        delete d_ptr->config;
-        d_ptr->config = 0;
-    }
-
-    *d_ptr = *other.d_ptr;
-    if (other.d_ptr->config)
-        d_ptr->config = other.d_ptr->config->copy();
-
-    return *this;
-}
 
 /*!
     \fn void QEasingCurve::swap(QEasingCurve &other)

src/corelib/tools/qeasingcurve.h

@@ -82,7 +82,8 @@ public:
     QEasingCurve(const QEasingCurve &other);
     ~QEasingCurve();
 
-    QEasingCurve &operator=(const QEasingCurve &other);
+    QEasingCurve &operator=(const QEasingCurve &other)
+    { if ( this != &other ) { QEasingCurve copy(other); swap(copy); } return *this; }
 #ifdef Q_COMPILER_RVALUE_REFS
     QEasingCurve(QEasingCurve &&other) : d_ptr(other.d_ptr) { other.d_ptr = 0; }
     QEasingCurve &operator=(QEasingCurve &&other)