pgsql: Make bms_prev_member work correctly with a 64 bit bitmapword

Make bms_prev_member work correctly with a 64 bit bitmapword

5c067521 erroneously had coded bms_prev_member assuming that a bitmapword
would always hold 32 bits and started it's search on what it thought was the
highest 8-bits of the word. This was not the case if bitmapwords were 64
bits.

In passing add a test to exercise this function a little. Previously there was
no coverage at all.

David Rowly

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/a5ab8928d7d9e2cf76ed0590efbd9795ea9e5b5e

Modified Files
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src/backend/nodes/bitmapset.c | 2 +-
src/test/regress/expected/partition_prune.out | 23 +++++++++++++++++++++++
src/test/regress/sql/partition_prune.sql | 25 +++++++++++++++++++++++++
3 files changed, 49 insertions(+), 1 deletion(-)