Small performance optimizations of the interpreter.

Short summary of the changes:
 - The ecma_reference_t is removed, and its helper functions are deleted.
 - The delete operation does not depend on ecma_reference_t anymore.
 - A new resolve function is added which returns the current value
   of a named binding in the context chain.
 - The vm_op_set_value does not perform type conversions when its arguments
   has the appropriate types.

JerryScript-DCO-1.0-Signed-off-by: Zoltan Herczeg zherczeg.u-szeged@partner.samsung.com

jerry-core/vm/opcodes.h

@@ -107,7 +107,7 @@ ecma_value_t
 vm_op_delete_prop (ecma_value_t, ecma_value_t, bool);
 
 ecma_value_t
-vm_op_delete_var (jmem_cpointer_t, ecma_object_t *, bool);
+vm_op_delete_var (jmem_cpointer_t, ecma_object_t *);
 
 ecma_collection_header_t *
 opfunc_for_in (ecma_value_t, ecma_value_t *);