systat: Handle SIGWINCH to properly window resizing and adjust -swap disk stat based on new size.

[ota_j.email.ne.jp]

Summary

Display corrupts after resizing a window.
Process SIGWINCH to redraw all window.

Test Plan

Start X Window and run systat in a terminal..
Then resize the window and check screen is redraws.

[mr]

Looks good and works for me.