pgsql: Remove "fuzzy comparison" logic in qsort comparison function for

Log Message:
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Remove "fuzzy comparison" logic in qsort comparison function for
choose_bitmap_and(). It was way too fuzzy --- per comment, it was meant to be
1% relative difference, but was actually coded as 0.01 absolute difference,
thus causing selectivities of say 0.001 and 0.000000000001 to be treated as
equal. I believe this thinko explains Maxim Boguk's recent complaint. While
we could change it to a relative test coded like compare_fuzzy_path_costs(),
there's a bigger problem here, which is that any fuzziness at all renders the
comparison function non-transitive, which could confuse qsort() to the point
of delivering completely wrong results. So forget the whole thing and just
do an exact comparison.

Modified Files:
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pgsql/src/backend/optimizer/path:
indxpath.c (r1.207 -> r1.208)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/indxpath.c.diff?r1=1.207&r2=1.208)