rust-status: move to recursive traversal to prepare for parallel traversal
I have looked into traversing the working directory in parallel either
by a recursive or an iterative algorithm. The recursive approach won quite
decisively both in terms of performance and code readability.
You can look at my experiment here:
The chance of a stack overflow happening because the directories get too nested
This change does not yet do anything in parallel.
Differential Revision: https://phab.mercurial-scm.org/D8215