Support for streaming large-files to disk.

[pmarkert]

Currently the save action can save a file to disk, however, the entire response must be buffered in memory because of the way actions are processed. Support an optional request property that will cause the response to be saved directly to the specified location on disk. Needs to check whether safe_mode is enabled or not before allowing the feature. If the response is streamed to disk, it will obviously not be available for response actions to inspect, however, maybe a property can be set to indicate the location to where the file was saved. Actions can then print/display that property value if needed.