pgsql: Speed up COPY into tables with DEFAULT nextval()

Speed up COPY into tables with DEFAULT nextval()

Previously the presence of a nextval() prevented the
use of batch-mode COPY.  This patch introduces a
special case just for nextval() functions. In future
we will introduce a general case solution for
labelling volatile functions as safe for use.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/4d1e2aeb1a162770683a8d1e13fc13ac2d95d810

Modified Files
--------------
src/backend/commands/copy.c          |   15 ++++-
src/backend/optimizer/util/clauses.c |  116 ++++++++++++++++++++++++++++++++++
src/include/optimizer/clauses.h      |    1 +
3 files changed, 130 insertions(+), 2 deletions(-)