Utils::FileName: Rename append to appendString()

The function's operation of simply appending the string as is would be
fine if FileNames were strings. But they aren't, so the function name
should be intentionally ugly to stand out.

Change-Id: I85e16844e2d69cacb6566c538182b84300c45161
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
BlackBerry: Enable selection of default API level

Task-number: QTCREATORBUG-11009

Change-Id: If11343a26134238854e64a0cf88ea91973615e69
Reviewed-by: David Kaspar <dkaspar@blackberry.com>
Reviewed-by: Mehdi Fekari <mfekari@blackberry.com>
Reviewed-by: Nicolas Arnaud-Cormos <nicolas@kdab.com>