pgsql: Allow named parameters to be specified using => in addition to :

Allow named parameters to be specified using => in addition to :=

SQL has standardized on => as the use of to specify named parameters,
and we've wanted for many years to support the same syntax ourselves,
but this has been complicated by the possible use of => as an operator
name.  In PostgreSQL 9.0, we began emitting a warning when an operator
named => was defined, and in PostgreSQL 9.2, we stopped shipping a
=>(text, text) operator as part of hstore.  By the time the next major
version of PostgreSQL is released, => will have been deprecated for a
full five years, so hopefully there won't be too many people still
relying on it.  We continue to support := for compatibility with
previous PostgreSQL releases.

Pavel Stehule, reviewed by Petr Jelinek, with a few documentation
tweaks by me.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/865f14a2d31af23a05bbf2df04c274629c5d5c4d

Modified Files
--------------
doc/src/sgml/func.sgml                        |    2 +-
doc/src/sgml/syntax.sgml                      |   21 ++++++--
doc/src/sgml/xfunc.sgml                       |    6 +--
src/backend/commands/operatorcmds.c           |   10 ----
src/backend/parser/gram.y                     |   11 +++-
src/backend/parser/scan.l                     |    6 +++
src/test/regress/expected/create_operator.out |    7 +--
src/test/regress/expected/polymorphism.out    |   67 +++++++++++++++++++++++++
src/test/regress/sql/create_operator.sql      |    2 +-
src/test/regress/sql/polymorphism.sql         |   16 ++++++
10 files changed, 124 insertions(+), 24 deletions(-)