nop90: 29/30 points

Comments:
I found that the following tasks were not implemented correctly or contained errors.

* Null pointers check doesn't work for methods:
  "
  class Main {
   void main() {
      A a;
	  a.m();
   }
  }
  class A {
   void m() { }
  }
  "
* Side effects
  If methods have side effects, then the execution order matters:
  "
  class Main {
   void main() {
  	  write(m1() + m2());
  	  writeln();
   }

   int m1() {
  	  write(1);
	  return 1;
   }

   int m2() {
	  write(2);
	  return 2;
   }
  }
  "
* Can't compile programs which use many registers