FR: Split folder and filename in file requesters

[fromwithin]

When doing a render, or any operation that creates a new file, the file requester shows up with the user options. In that window, the file and path are a single string. I find it a pain to always have to get the mouse in just the right place after the last directory to select just the filename when naming the files.

I request that the path and filename are split into separate boxes so that the filename is much easier to instantly see and change. It's very, very rare that the path needs to change; it's usually only when doing a final render and even then I find that rendering into the default Render folder and taking out the file manually is fine.