[qtcontacts-sqlite] Use less error-prone method of detecting privileges

This commit just attempts to mkpath on the privileged database
directory.  If it fails, it now assumes that it's nonprivileged.
This method is less error-prone than the existing method which
relies on Qt's FS permission support (which cannot be abstracted
perfectly across platforms, and so doesn't really work).
Merge pull request #133 from chriadam/privnext

[qtcontacts-sqlite] Use less error-prone method of detecting privileges