fixed problems with joined inheritance and composite keys

SchemaTool now creates all Id columns not just only the first one.
Insert statement for child entity now contains parameter for additional key columns only once.
inheritance with composite keys

added tests for single table inheritance
Adding EntityManagerDecorator base class as an extension point for EntityManager
[DDC-2426] Missing length attribute in doctrine-mapping.xsd for <id> tag.
Merge branch 'DDC-2426'
[DDC-2267] Allow EntityManager#flush($entity) to be called on entities scheduled for removal.
Merge branch 'DDC-2267'
Merge pull request #537 from Powerhamster/joined-composite-keys

fixed problems with joined inheritance and composite keys
Merge pull request #524 from lstrojny/feature/entity-manager-decorator

EntityManagerDecorator base class as an extension point for EntityManager