in the save dialog, when popping up the 'browse' dialog it gets
the right directory, but after changing directories the result
passed back to the save directory is wrong.

This looks like it's because we pass set_current_directory()
into the dialog but use get_filename() to pull the results.

Note that the pan-file-entry dialog can be used for both file
and directory selection, so we ought to key off of the gtkfilechooser
action mode to decide whether to use the filename or directory API calls.