[ Ken VanDine ] * Adds support for multiple handler types: source, destination and share. Enforce single transfer per peer, if a second transfer request is made from a peer that already has an unfinished transfer, cancel the previous one. This is needed as long as apps are required to be single instance. * If the transfer isn't persistent, attempt to hardlink instead of copying. If the link fails, fallback to a copy. * If the default source is set to anything other than a click appId triplet, fallback to the legacy APP_ID. Changed default source for contacts to the legacy APP_ID for address-book-app