allow to do git command on directory not owned by the process

See https://github.com/git/git/commit/8959555cee7ec045958f9b6dd62e541affb7e7d9

re6st/version.py

 import subprocess as _S
-from os.path import dirname as _d
-_d = _d(__file__)
+import os.path as _P
+_d = _P.realpath(_P.dirname(_P.dirname(__file__)))
 
 def _git_call(*args):
-    return _S.call(("git",) + args, cwd=_d)
+    return _S.call(("git", "-c", "safe.directory=" + _d) + args, cwd=_d)
 
 def _git_output(*args):
-    p = _S.Popen(("git",) + args, cwd=_d, stdout=_S.PIPE, stderr=_S.PIPE)
+    p = _S.Popen(
+            ("git", "-c", "safe.directory=" + _d) + args,
+            cwd=_d,
+            stdout=_S.PIPE,
+            stderr=_S.PIPE)
     out, err = p.communicate()
     if p.returncode:
         raise _S.CalledProcessError(p.returncode, "git", err)