Repair VACUUM FULL bug introduced by HOT patch: the original way of

 Repair VACUUM FULL bug introduced by HOT patch: the original way of
 calculating a page's initial free space was fine, and should not have been
 "improved" by letting PageGetHeapFreeSpace do it.  VACUUM FULL is going to
 reclaim LP_DEAD line pointers later, so there is no need for a guard
 against the page being too full of line pointers, and having one risks
 rejecting pages that are perfectly good move destinations.
 
 This also exposed a second bug, which is that the empty_end_pages logic
 assumed that any page with no live tuples would get entered into the
 fraged_pages list automatically (by virtue of having more free space than
 the threshold in the do_frag calculation).  This assumption certainly
 seems risky when a low fillfactor has been chosen, and even without
 tunable fillfactor I think it could conceivably fail on a page with many
 unused line pointers.  So fix the code to force do_frag true when notup
 is true, and patch this part of the fix all the way back.
 
 Per report from Tomas Szepe.