Add upgrade script

htdocs/install/mysql/migration/3.5.0-3.6.0.sql

+--
+-- Be carefull to requests order.
+-- This file must be loaded by calling /install/index.php page
+-- when current version is 3.5.0 or higher. 
+--
+-- To rename a table:       ALTER TABLE llx_table RENAME TO llx_table_new;
+-- To add a column:         ALTER TABLE llx_table ADD COLUMN newcol varchar(60) NOT NULL DEFAULT '0' AFTER existingcol;
+-- To rename a column:      ALTER TABLE llx_table CHANGE COLUMN oldname newname varchar(60);
+-- To drop a column:        ALTER TABLE llx_table DROP COLUMN oldname;
+-- To change type of field: ALTER TABLE llx_table MODIFY COLUMN name varchar(60);
+-- To drop a foreign key:   ALTER TABLE llx_table DROP FOREIGN KEY fk_name;
+-- To restrict request to Mysql version x.y use -- VMYSQLx.y
+-- To restrict request to Pgsql version x.y use -- VPGSQLx.y
+-- To make pk to be auto increment (mysql):   VMYSQL4.3 ALTER TABLE llx_c_shipment_mode CHANGE COLUMN rowid rowid INTEGER NOT NULL AUTO_INCREMENT;
+-- To make pk to be auto increment (postgres) VPGSQL8.2 NOT POSSIBLE. MUST DELETE/CREATE TABLE
+
+-- -- VPGSQL8.2 DELETE FROM llx_usergroup_user      WHERE fk_user      NOT IN (SELECT rowid from llx_user);
+-- -- VMYSQL4.1 DELETE FROM llx_usergroup_user      WHERE fk_usergroup NOT IN (SELECT rowid from llx_usergroup);
+
+