Avoid unnecessary copying in copyIn

Only re-use the existing reference if
it is large enough to hold all the new data.
If it isn't then throw it away to avoid
copying its current contents during
the resize().

pvDataApp/pv/pvData.h

@@ -1319,6 +1319,10 @@ public:
     {
         svector data;
         this->swap(data);
+        // Will have to re-alloc anyway? If so avoid copying
+        // data which will only be over-written
+        if(data.capacity()<len)
+            data.clear();
         data.resize(len);
         castUnsafeV(len, typeCode, (void*)data.data(), id, ptr);
         this->swap(data);