cmd: By default, on linux, the parent file handles will be closed to …

…leave the child less cluttered, and make it easier to debug as it will only have the file descriptors we set. It appears to be more stable regarding the stdin-is-closed-but-child-doesn't-realize-this issue

lib/git/cmd.py

@@ -215,6 +215,7 @@ def execute(self, command,
                                 stdin=istream,
                                 stderr=subprocess.PIPE,
                                 stdout=subprocess.PIPE,
+                                close_fds=(os.name=='posix'),# unsupported on linux
                                 **extra
                                 )
         if as_process: