libpacman: Disabled _pacman_sortbydeps, it does not affect tests and will be rewritten.
libpacman: Remove _pacman_sortbydeps mode, new graph coloring code should have enought information to produce a properly ordered package transaction order.
libpacman: Finally able to RIP pmtrans_t::_packages.
libpacman: Make _pacman_trans_add handle an upgrade which is actually an install only.