QList: iterate forward in contains()

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: Id2388eab2339c24deb93095495d87056a9c57133
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qvector.h

@@ -791,10 +791,10 @@ int QVector<T>::lastIndexOf(const T &t, int from) const
 template <typename T>
 bool QVector<T>::contains(const T &t) const
 {
-    T* b = d->begin();
-    T* i = d->end();
-    while (i != b)
-        if (*--i == t)
+    T* i = d->begin();
+    T* e = d->end();
+    for (; i != e; ++i)
+        if (*i == t)
             return true;
     return false;
 }