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.

src/test/regress/expected/create_operator.out

@@ -29,13 +29,14 @@ CREATE OPERATOR #%# (
 -- Test comments
 COMMENT ON OPERATOR ###### (int4, NONE) IS 'bad right unary';
 ERROR:  operator does not exist: integer ######
--- Show deprecated message. => is deprecated now
+-- => is disallowed now
 CREATE OPERATOR => (
    leftarg = int8,		-- right unary
    procedure = numeric_fac
 );
-WARNING:  => is deprecated as an operator name
-DETAIL:  This name may be disallowed altogether in future versions of PostgreSQL.
+ERROR:  syntax error at or near "=>"
+LINE 1: CREATE OPERATOR => (
+                        ^
 -- Should fail. CREATE OPERATOR requires USAGE on SCHEMA
 BEGIN TRANSACTION;
 CREATE ROLE regress_rol_op1;

src/test/regress/expected/polymorphism.out

@@ -1356,6 +1356,73 @@ select dfunc('a'::text, 'b', flag := true); -- mixed notation
  a
 (1 row)
 
+-- ansi/sql syntax
+select dfunc(a => 1, b => 2);
+ dfunc 
+-------
+     1
+(1 row)
+
+select dfunc(a => 'a'::text, b => 'b');
+ dfunc 
+-------
+ a
+(1 row)
+
+select dfunc(a => 'a'::text, b => 'b', flag => false); -- named notation
+ dfunc 
+-------
+ b
+(1 row)
+
+select dfunc(b => 'b'::text, a => 'a'); -- named notation with default
+ dfunc 
+-------
+ a
+(1 row)
+
+select dfunc(a => 'a'::text, flag => true); -- named notation with default
+ dfunc 
+-------
+ a
+(1 row)
+
+select dfunc(a => 'a'::text, flag => false); -- named notation with default
+ dfunc 
+-------
+ 
+(1 row)
+
+select dfunc(b => 'b'::text, a => 'a', flag => true); -- named notation
+ dfunc 
+-------
+ a
+(1 row)
+
+select dfunc('a'::text, 'b', false); -- full positional notation
+ dfunc 
+-------
+ b
+(1 row)
+
+select dfunc('a'::text, 'b', flag => false); -- mixed notation
+ dfunc 
+-------
+ b
+(1 row)
+
+select dfunc('a'::text, 'b', true); -- full positional notation
+ dfunc 
+-------
+ a
+(1 row)
+
+select dfunc('a'::text, 'b', flag => true); -- mixed notation
+ dfunc 
+-------
+ a
+(1 row)
+
 -- check reverse-listing of named-arg calls
 CREATE VIEW dfview AS
    SELECT q1, q2,

src/test/regress/sql/create_operator.sql

@@ -35,7 +35,7 @@ CREATE OPERATOR #%# (
 -- Test comments
 COMMENT ON OPERATOR ###### (int4, NONE) IS 'bad right unary';
 
--- Show deprecated message. => is deprecated now
+-- => is disallowed now
 CREATE OPERATOR => (
    leftarg = int8,		-- right unary
    procedure = numeric_fac

src/test/regress/sql/polymorphism.sql

@@ -748,6 +748,22 @@ select dfunc('a'::text, 'b', flag := false); -- mixed notation
 select dfunc('a'::text, 'b', true); -- full positional notation
 select dfunc('a'::text, 'b', flag := true); -- mixed notation
 
+-- ansi/sql syntax
+select dfunc(a => 1, b => 2);
+select dfunc(a => 'a'::text, b => 'b');
+select dfunc(a => 'a'::text, b => 'b', flag => false); -- named notation
+
+select dfunc(b => 'b'::text, a => 'a'); -- named notation with default
+select dfunc(a => 'a'::text, flag => true); -- named notation with default
+select dfunc(a => 'a'::text, flag => false); -- named notation with default
+select dfunc(b => 'b'::text, a => 'a', flag => true); -- named notation
+
+select dfunc('a'::text, 'b', false); -- full positional notation
+select dfunc('a'::text, 'b', flag => false); -- mixed notation
+select dfunc('a'::text, 'b', true); -- full positional notation
+select dfunc('a'::text, 'b', flag => true); -- mixed notation
+
+
 -- check reverse-listing of named-arg calls
 CREATE VIEW dfview AS
    SELECT q1, q2,