Doc: Improve docs for file permission checking on NTFS

- Reduce verbosity in qfiledevice.cpp
- Copy to qfileinfo.cpp

Task-number: QTBUG-35232
Change-Id: I4b0de36bdf266ebf486f73daecec8fbb74fa1d4c
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>

src/corelib/io/qfiledevice.cpp

@@ -139,10 +139,9 @@ void QFileDevicePrivate::setError(QFileDevice::FileError err, int errNum)
     are returned and on Windows the rights of the current user are
     returned. This behavior might change in a future Qt version.
 
-    Note that Qt does not by default check for permissions on NTFS
-    file systems, as this may decrease the performance of file
-    handling considerably. It is possible to force permission checking
-    on NTFS by including the following code in your source:
+    \note On NTFS file systems, ownership and permissions checking is
+    disabled by default for performance reasons. To enable it,
+    include the following line:
 
     \snippet ntfsp.cpp 0
 

src/corelib/io/qfileinfo.cpp

@@ -271,6 +271,17 @@ QDateTime &QFileInfoPrivate::getFileTime(QAbstractFileEngine::FileTime request)
     groupId(). You can examine a file's permissions and ownership in a
     single statement using the permission() function.
 
+    \note On NTFS file systems, ownership and permissions checking is
+    disabled by default for performance reasons. To enable it,
+    include the following line:
+
+    \snippet ntfsp.cpp 0
+
+    Permission checking is then turned on and off by incrementing and
+    decrementing \c qt_ntfs_permission_lookup by 1.
+
+    \snippet ntfsp.cpp 1
+
     \section1 Performance Issues
 
     Some of QFileInfo's functions query the file system, but for