Merge Resdom nodes into TargetEntry nodes to simplify code and save a

Merge Resdom nodes into TargetEntry nodes to simplify code and save a
few palloc's.  I also chose to eliminate the restype and restypmod fields
entirely, since they are redundant with information stored in the node's
contained expression; re-examining the expression at need seems simpler
and more reliable than trying to keep restype/restypmod up to date.

initdb forced due to change in contents of stored rules.