Sorting directories before files in tree view

[John Keeping]

On Fri, Jul 21, 2017 at 09:13:33PM +0530, John wrote:
> Is this possible?.

Not without significant changes to ui-tree.c.  Currently we output items
in the order they appear in the tree object being displayed (by
definition, this is lexicographically sorted).  Displaying them in a
different order would require saving all of the items in memory and then
sorting them before display.