pgsql: Use a fresh copy of query_list when making a second plan in GetC

Use a fresh copy of query_list when making a second plan in GetCachedPlan.

The code path that tried a generic plan, didn't like it, and then made a
custom plan was mistakenly passing the same copy of the query_list to the
planner both times. This doesn't work too well for nontrivial queries,
since the planner tends to scribble on its input. Diagnosis and fix by
Yamamoto Takashi.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/21fb95da46bce8de3e149707c680d489b8a5ffb0

Modified Files
--------------
src/backend/utils/cache/plancache.c | 10 +++++++++-
1 files changed, 9 insertions(+), 1 deletions(-)