Merge branch 'js/mingw-loosen-overstrict-tree-entry-checks'

Merge branch 'js/mingw-loosen-overstrict-tree-entry-checks'

An earlier update to Git for Windows declared that a tree object is
invalid if it has a path component with backslash in it, which was
overly strict, which has been corrected.  The only protection the
Windows users need is to prevent such path (or any path that their
filesystem cannot check out) from entering the index.

* js/mingw-loosen-overstrict-tree-entry-checks:
  mingw: only test index entries for backslashes, not tree entries