pgsql: The rolled-back flag on serializable xacts was pointless and red

The rolled-back flag on serializable xacts was pointless and redundant with
the marked-for-death flag. It was only set for a fleeting moment while a
transaction was being cleaned up at rollback. All the places that checked
for the rolled-back flag should also check the marked-for-death flag, as
both flags mean that the transaction will roll back. I also renamed the
marked-for-death into "doomed", which is a lot shorter name.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/264a6b127a918800d9f8bac80b5f4a8a8799d0f1

Modified Files
--------------
src/backend/storage/lmgr/predicate.c      |   52 +++++++++++++---------------
src/include/storage/predicate_internals.h |   11 +++---
2 files changed, 29 insertions(+), 34 deletions(-)