Some fixes for DECSC/DECRC behavior

This PR fixes the following problems.

- Some duplicated code evaluating DECSC/DECRC are found.
- ISO-2022 charcter bank state is not saved/restored with DECSC/DECRC
  (show the VTTEST result)
![2014-02-19 22 14 43](https://f.cloud.github.com/assets/1162739/2206744/2f904f78-9968-11e3-871d-80437416155d.png)
- Origin mode and wrap-around mode are not saved/restored with DECSC/DECRC
  (show http://www.vt100.net/docs/vt510-rm/DECSC)