Fix drag and drop file target location

[seth--]

http://i.imgur.com/AdKl0ot.png

If I want to copy a file from the left to the right panel, the natural way for me is draging and droping it to the place where the yellow point is.

With spacefm the file will be copied inside the src folder without any indication. I think this will fix it:

• If the file is dropped where there is no text, it should be copied to the open folder. If it's droped over the "src" text, it should be copied to the subfolder.

• If the file will be copied into a subfolder, the subfolder name should be highlighted. (independentenly of the previous point being accepted).

  IIRC dolphin works that way.

[IgnorantGuru]

If you drop into the Size or other columns, it will go into the current folder rather than the subfolder. This is default GTK behavior and no plan to change this. Thanks for the feedback.