Added a case for parseATTime, and a bugfix

Change to graphite.render.attime.parseATTime() to allow graphlot's HH:MM_YYYYmmdd format to be properly converted when tries to find events in a certain absolute range.

NOTE: The format I use doesn't have an underscore, because it is stripped off previously and I wanted to make as minimal of a change as possible.

Also, fixed a bug in the /metrics/expand controller, where a property was mis-referenced.