pgsql: Change tqual.c tests to use !TransactionIdIsCurrentTransactionId,

Log Message:
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Change tqual.c tests to use !TransactionIdIsCurrentTransactionId, rather than
TransactionIdDidAbort, when handling the case that xmin is one of the current
transaction's XIDs and the tuple has been deleted. xmax must also be one of
the current transaction's XIDs, since no one else can see it yet, and it's
cheaper to look at local state than shared state to find out if xmax aborted.
Per an idea of Heikki's.

Modified Files:
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pgsql/src/backend/utils/time:
tqual.c (r1.105 -> r1.106)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/time/tqual.c?r1=1.105&r2=1.106)