Fix/unupdated x dict

[ktaaaki]

This is fix of IterativeLoss. (hot fix #114 is closed.)

Issue: a bug of IterativeLoss

1. x_dict.update({value: x_dict[key]}) at line:156 register key-variable's value as value-variable's value. And key-variable remains.
2. At next step, key-variable are sometimes overwritten but sometimes not. For example, AddLoss copies an input dictionary, and overwrite old one to updated one.
3. the key-variable is not updated. So the effect of reccurence is ignored.

Solution

• delete future variable by replace_dict_keys at the step of IterativeLoss.
• get only updated variables from distribution.sample or loss.eval and override them to dictionary of all variables.
• fix some illegal operations to input dictionary
• fix wrong input_var of some losses