bug#3359: 23.0.94; vc-dir:git backend bug

[Zale Yu]

Hi, All:
   STEPs to reproduce this bug:
   1. Create a empty git repo /tmp/myrepo
   2.  Add /tmp/myrepo/subdir/HELLO to git repo
   3.  Commit
   4. edit /tmp/myrepo/subdir/HELLO
   5. vc-dir /tmp/myrepo/subdir
        the *vc-dir* buffer reads:
        ==========================
VC backend : Git
Working dir: /tmp/myrepo/subdir/
Branch     : master

                         ./
                         subdir/
     edited              subdir/HELLO  /*  PRESS f here */
        ==========================
    6.   press f at the line "edited ....." emacs try to open file:
/tmp/myrepo/subdir/subdir/HELLO
--