pgsql: Fix btmarkpos/btrestrpos to handle array keys.

Fix btmarkpos/btrestrpos to handle array keys.

This fixes another error in commit 9e8da0f75731aaa7605cf4656c21ea09e84d2eb1.
I neglected to make the mark/restore functionality save and restore the
current set of array key values, which led to strange behavior if an
IndexScan with ScalarArrayOpExpr quals was used as the inner side of a
mergejoin. Per bug #7570 from Melese Tesfaye.

Branch
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REL9_2_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/f2366e584aea41b980f23fcf0a2e118efd7fb09b

Modified Files
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src/backend/access/nbtree/nbtree.c | 8 ++++
src/backend/access/nbtree/nbtutils.c | 59 ++++++++++++++++++++++++++++++++++
src/include/access/nbtree.h | 3 ++
3 files changed, 70 insertions(+), 0 deletions(-)