pgsql: Fix oversight in recent parameterized-path patch.

Fix oversight in recent parameterized-path patch.

bitmap_scan_cost_est() has to be able to cope with a BitmapOrPath, but
I'd taken a shortcut that didn't work for that case.  Noted by Heikki.
Add some regression tests since this area is evidently under-covered.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/7c85aa39fc08df44e1ce67e651bda4cf7e331580

Modified Files
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src/backend/optimizer/path/indxpath.c      |   13 ++++---
src/test/regress/expected/create_index.out |   51 ++++++++++++++++++++++++++++
src/test/regress/sql/create_index.sql      |   16 +++++++++
3 files changed, 75 insertions(+), 5 deletions(-)