Small grammar fix

The exception was reading 

```
A detached entity was found during {removed|persisted} [entityName] 
```

I changed the verbs to infinitive now. Alternatively, the text in ``ORMInvalidArgumentException::detachedEntityCannot`` could also be changed to read 


```
Detached entity [entityName] cannot be {removed|persisted}  
```

lib/Doctrine/ORM/UnitOfWork.php

@@ -1655,7 +1655,7 @@ private function doPersist($entity, array &$visited)
 
             case self::STATE_DETACHED:
                 // Can actually not happen right now since we assume STATE_NEW.
-                throw ORMInvalidArgumentException::detachedEntityCannot($entity, "persisted");
+                throw ORMInvalidArgumentException::detachedEntityCannot($entity, "persist");
 
             default:
                 throw new UnexpectedValueException("Unexpected entity state: $entityState." . self::objToStr($entity));
@@ -1726,7 +1726,7 @@ private function doRemove($entity, array &$visited)
                 break;
 
             case self::STATE_DETACHED:
-                throw ORMInvalidArgumentException::detachedEntityCannot($entity, "removed");
+                throw ORMInvalidArgumentException::detachedEntityCannot($entity, "remove");
             default:
                 throw new UnexpectedValueException("Unexpected entity state: $entityState." . self::objToStr($entity));
         }