another way to fix the problem described in #693

This ticket is trying to fix the issue described in https://github.com/propelorm/Propel/pull/693, with different approach. 
Before this patch, propel will generate sql as follow:
```sql
DROP TABLE IF EXISTS "foo"."foo"."issue693_version" CASCADE;

CREATE TABLE "foo"."foo"."issue693_version"
(
    "id" INTEGER NOT NULL,
    "bar" INTEGER,
    "version" INTEGER DEFAULT 0 NOT NULL,
    PRIMARY KEY ("id","version")
);
```

In the Peer class
```php
const ID = 'foo.foo.issue693_version.id';
const BAR = 'foo.foo.issue693_version.bar';
const VERSION = 'foo.foo.issue693_version.version';
```