Properly format the error message during unintended switches.

* subversion/libsvn_client/cmdline/switch.c
  (switch_internal): Use 'svn_dirent_local_style' instead of
    'svn_dirent_dirname' when formatting the "no common ancestry" error message.

Patch by: Evgeny Kotkov <evgeny.kotkov{_AT_}visualsvn.com>