[arch-dev-public] adding xdelta3 to repo

Hi, I am going to add xdelta3 to the repos. It is a separate developmental branch to xdelta(1) that has recently been declared stable. xdelta3 can be installed alongside xdelta and following other distros it is probably best to have this as a separate package. Finally, xdelta3 is needed for the reworked delta implementation in pacman. Thanks for you lack of objection... Allan