New windows are created with the contents of the latest-modified unsaved content

[cbowns]

When any number of windows are open with unsaved content, and you open a new window, save-session adds a new file to the new window, and pre-populates that file with the contents of whatever unsaved file was most recently modified.

Configuration: Atom 1.2.0 and save-session 0.15.7

(Parent issue: #146)