QVector: iterate forward in operator==

After much head-scratching, we found no reason for the backwards iteration.
Indeed, forward iteration should be slightly faster than backwards, because
it operates in the direction in which cache-lines are filled, usually.

This is in preparation of using std algorithms instead of hand-written
loops. It avoids having to use std::reverse_iterator.

Change-Id: I180c52e0bb90e823216b77d3f49f2a3fd395567d
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qvector.h

@@ -707,11 +707,11 @@ bool QVector<T>::operator==(const QVector<T> &v) const
         return true;
     if (d->size != v.d->size)
         return false;
-    T* b = d->begin();
-    T* i = b + d->size;
-    T* j = v.d->end();
-    while (i != b)
-        if (!(*--i == *--j))
+    T* e = d->end();
+    T* i = d->begin();
+    T* vi = v.d->begin();
+    for (; i != e; ++i, ++vi)
+        if (!(*i == *vi))
             return false;
     return true;
 }