1. Added new EXECUTE BLOCK statement

2. Added 	default paremeters in stored procedures

doc/sql.extensions/README.default_parameters

@@ -0,0 +1,108 @@
+SQL Language Extension: default paremeters in stored procedures
+
+Function:
+	allow input parameters of stored procedures to have optional default values
+
+Autor:
+	Vlad Horsun <horsun at kdb.dp.ua>
+
+Syntax:
+	same as default value definition of column or domain, except that
+you can use '=' in place of 'DEFAULT' keyword. Parameters with default values 
+must be last in parameter list i.e. not allowed to define parameter without 
+default value after parameter with default value. Caller must set first few 
+parameters, i.e. not allowed set param1, param2, miss param3, set param4...
+
+
+Default values substitution occurs at run-time. If you define procedure with 
+defaults (say P1), call it from another procedure (say P2) and skip some last 
+parameters (with default value) then default values for P1 will be substituted 
+by the engine at time of the beginning of execution P1. Then if you change 
+default values for P1 it is not need to recompile P2. But it is still necessary 
+to disconnect all client connections, for more details see IB6 Beta documentation 
+"Data Definition Guide", section "Altering and dropping procedures in use"
+
+
+Examples:
+
+CONNECT ... ;
+
+CREATE PROCEDURE P1 (X INTEGER = 123)
+RETURNS (Y INTEGER)
+AS
+BEGIN
+  Y = X;
+  SUSPEND;
+END;
+COMMIT;
+
+ SELECT * FROM P1;
+
+           Y
+============
+
+         123
+
+EXECUTE PROCEDURE P1;
+
+           Y
+============
+         123
+
+
+CREATE PROCEDURE P2
+RETURNS (Y INTEGER)
+AS
+BEGIN
+  FOR SELECT Y FROM P1 INTO :Y
+  DO SUSPEND;
+END;
+COMMIT;
+
+
+SELECT * FROM P2;
+
+           Y
+============
+
+         123
+
+
+ALTER PROCEDURE P1 (X INTEGER = CURRENT_TRANSACTION)
+         RETURNS (Y INTEGER)
+AS
+BEGIN
+  Y = X;
+  SUSPEND;
+END;
+COMMIT;
+
+SELECT * FROM P1;
+
+           Y
+============
+
+        5875
+
+SELECT * FROM P2;
+
+           Y
+============
+
+         123
+
+COMMIT;
+
+CONNECT  ... ;
+
+SELECT * FROM P2;
+
+           Y
+============
+
+        5880
+
+
+Notes:
+	default sources and BLR's are kept in RDB$FIELDS
+

doc/sql.extensions/README.execute_block

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+SQL Language Extension: EXECUTE BLOCK
+
+Function:
+	Allow execute PL-SQL block as if it is stored procedure. 
+	Supports input and output parameters
+
+Autor:
+	Vlad Horsun <horsun@kdb.dp.ua>
+
+Syntax:
+	EXECUTE BLOCK [ (param datatype = ?, param datatype = ?, ...) ]
+		[ RETURNS (param datatype, param datatype, ...) }
+	AS
+	[DECLARE VARIABLE var datatype; ...]
+	BEGIN
+	...
+	END
+
+Client-side:
+	The call isc_dsql_sql_info with parameter isc_info_sql_stmt_type returns
+	- isc_info_sql_stmt_select, if block has output parameters. 
+	Semantics of a call is similar to SELECT query - client has open cursor, 
+can fetch data from it, and must close it after use.
+
+	- isc_info_sql_stmt_exec_procedure, if block has no output parameters.
+	Semantics of a call is similar to EXECUTE query - client has no cursor,
+execution runs until first SUSPEND or end of block
+
+	The client should preprocess only head of the SQL statement or use '?' 
+instead of ':' as parameter indicator because in a body of the block may be links 
+to local variables and \ or parameters with a colon ahead.
+
+Example:
+	User SQL is
+		EXECUTE BLOCK (X INTEGER = :X) RETURNS (Y VARCHAR)
+		AS
+		DECLARE V INTEGER;
+		BEGIN
+		  INSERT INTO T(...) VALUES (... :X ...);
+
+		  SELECT ... FROM T INTO :Y;
+		  SUSPEND;
+		END
+	
+	Preprocessed SQL is
+		EXECUTE BLOCK (X INTEGER = ?) RETURNS (Y VARCHAR)
+		AS
+		DECLARE V INTEGER;
+		BEGIN
+		  INSERT INTO T(...) VALUES (... :X ...);
+
+		  SELECT ... FROM T INTO :Y;
+		  SUSPEND;
+		END
+