Fixing of bugs according to FindBug report

Guys,

I run FindBug agains OrientDB code and found 100+ different bugs.
This PR contains fixes for some of them, which were considered by me safe.

But there are some additional thoughts:

ODatabaseCompare has multiple problems. Just take a look into method compareSchama().

Multiple usage of something like "new ArrayList<Map.Entry>(hashMap.entrySet())". That might lead to problems with data consistency, because according to JDK 1.6 Map implementations can reuse the same Entry object for iterations.

Multiple incorect handling of equal(). For example: OScriptGraphWrapper.equal():
```java
public boolean equals(Object obj) {
    return graph.equals(obj);
  }
```

If you have time, I recommend to take a look into FindBug report too.

ATTENTION: tests are passing, but, please, take a look...