PORTING_INFO

 * add rule
 *  p = direct literal; always < 0 for installed rpm rules
 *  d, if < 0 direct literal, if > 0 offset into whatprovides, if == 0 rule is assertion (look at p only)
 *
 *
 * A requires b, b provided by B1,B2,B3 => (-A|B1|B2|B3)
 *
 * p < 0 : pkg id of A
 * d > 0 : Offset in whatprovidesdata (list of providers of b)
 *
 * A conflicts b, b provided by B1,B2,B3 => (-A|-B1), (-A|-B2), (-A|-B3)
 * p < 0 : pkg id of A
 * d < 0 : Id of solvable (e.g. B1)
 *
 * d == 0: unary rule, assertion => (A) or (-A)
 *
 *   Install:    p > 0, d = 0   (A)             user requested install
 *   Remove:     p < 0, d = 0   (-A)            user requested remove (also: uninstallable)
 *   Requires:   p < 0, d > 0   (-A|B1|B2|...)  d: <list of providers for requirement of p>
 *   Updates:    p > 0, d > 0   (A|B1|B2|...)   d: <list of updates for solvable p>
 *   Conflicts:  p < 0, d < 0   (-A|-B)         either p (conflict issuer) or d (conflict provider) (binary rule)
 *                                              also used for obsoletes
 *   ?:          p > 0, d < 0   (A|-B)
 *   No-op ?:    p = 0, d = 0   (null)          (used as policy rule placeholder)
 *
 *   resulting watches:
 *   ------------------
 *   Direct assertion (no watch needed)( if d <0 ) --> d = 0, w1 = p, w2 = 0
 *   Binary rule: p = first literal, d = 0, w2 = second literal, w1 = p
 *   every other : w1 = p, w2 = whatprovidesdata[d];
 *   Disabled rule: w1 = 0
 *
 *   always returns a rule for non-rpm rules



p > 0, d = 0, (A), w1 = p, w2 = 0
p < 0, d = 0, (-A), w1 = p, w2 = 0
p !=0, d = 0, (p|q), w1 = p, w2 = q