Allow customization of qDebug output at runtime

Allow customization of qDebug output at runtime

Check the QT_OUTPUT_PATTERN environment variable in the default
message handler to customize the output of messages. Following
place holders are right now supported:
 %{message}, %{type}, %{file}, %{line}, %{function}

The original cleanupFuncinfo was written by Thiago Macieira.

Change-Id: I6ad25baaa0e6a1c9f886105d2a93ef3310e512a9
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: David Faure <faure@kde.org>