fixing issue 6121 by introducing flag denoting whether we're already trying to save a document
adding couple of comments for readability
adding unit test to verify that a saved untitled document can be saved again without prompting for Save As
updating unit test to reflect issue
moving cleanup to .always() per code review
Merge remote-tracking branch 'origin/master' into bchin/issue-6121
Merge pull request #7083 from adobe/bchin/issue-6121

Fixed issue #6121 - "Hitting Cmd-S immediately after saving an untitled file does another save as"