Accessibility: Small improvement to graphic link markup for adding an image

When using a screen reader to browse the page, the graphical link displayed below a textarea element is not tagged properly. While the anchor tag has a title, the embedded img tag does not have either a title or alt attribute. However since the img tag is embedded, screen readers prefer its information over the anchor tag's title attribute.
This results in the image's src link being broken down into the most useful pieces due to lack of other information.
The patch I'm attaching fixes this by providing a short alt tag that explains what the link does.