Backspace, left and right in Windows integrated terminal cause prompt to go out of sync in Git bash

- VSCode Version: 1.2.0-insider
- OS Version: Windows 10
- Terminal: Git bash

Steps to Reproduce:
1. Invoke the new integrated terminal
2. type command
3. backspace to delete some characters
4. Notice that while the command executed will be accurate to what was typed, the display of the line will be out of sync with the internal state of the terminal.
