JIT_F0 like JIT_R0 is hardcoded as temporary.

  Currently only used in store{i,r} but may be used in other places
were a scratch float register is required.
Add basic support for class inheritance and class methods.

  Some notes:
o The language only supports single inheritance.
o All methods are virtual.
o All fields are public.
o It supports a special syntax for calling explicit methods. For example,
  to call the declared, not the actual type one could write:
	class a_t ...;
	a_t var;
	var.a_t.method(...);
  This allows calling methods from superclasses.

  As of this commit there are some known problems:
o The code expects pointers to be either null or a compatible type.
  The code to check values upon assignment is still a todo, so for
  now it is easy to crash the vm by assigning an invalid type.
o Class objects should call the constructor, if any upon instantiation.
  This has not been implemented yet.