pgsql: Eliminate duplicate hasnulls bit testing in index tuple access,

Log Message:
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Eliminate duplicate hasnulls bit testing in index tuple access, and
clean up itup.h a little bit.

Modified Files:
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pgsql/src/backend/access/common:
indextuple.c (r1.73 -> r1.74)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/common/indextuple.c.diff?r1=1.73&r2=1.74)
pgsql/src/include/access:
itup.h (r1.42 -> r1.43)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/access/itup.h.diff?r1=1.42&r2=1.43)

Removed Files:
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pgsql/src/include/access:
ibit.h
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/access/ibit.h)