pgsql: When building a bitmap scan, must copy the bitmapqualorig

Log Message:
-----------
When building a bitmap scan, must copy the bitmapqualorig expression tree
to avoid sharing substructure with the lower-level indexquals.  This is
currently only an issue if there are SubPlans in the indexquals, which is
uncommon but not impossible --- see bug #2218 reported by Nicholas Vinen.
We use the same kluge for indexqual vs indexqualorig in the index scans
themselves ... would be nice to clean this up someday.

Modified Files:
--------------
    pgsql/src/backend/optimizer/plan:
        createplan.c (r1.206 -> r1.207)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/plan/createplan.c.diff?r1=1.206&r2=1.207)