Deprecate the ability to change the FS encoding separate from the locale

Deprecate the ability to change the FS encoding separate from the locale

Changing the encoding used by filenames separately from the locale
encoding is a broken concept and cannot work properly. This creates
ambiguity depending on the data source and how it's being treated.

Instead, enforce that the locale encoding is the only possibility to
deal with file names.

The QFile::encodeName and decodeName functions are retained due to the
Mac-specific issues and due to the sheer number of current
uses. There's no point in deprecating them and moving away from them.

Change-Id: Iedb2d8715d166a59a824f05bc11d107fd44f9c17
Discussed-on: http://lists.qt-project.org/pipermail/development/2012-May/003782.html
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>