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
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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/2b44a2d62d12406da59fa6b23a0854d1d5068b17

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