Be even less greedy

[fwenzel]

When UpShot processes a screenshot, it moves it to the dropbox folder. If you move it back to Desktop from there, it'll reprocess the file because it still carries the same metadata.

UpShot should probably either remove the screenshot metadata or add its own flag (something like UpShotProcessed: 1) to avoid this.

[fwenzel]

This patch parses the date out of screenshot files (Screen Shot 2014-08-04 at 9.24.18 AM.png, for instance) and if that's too old, it won't touch the file.