Move empty config creation code from svn to libsvn_subr and use it
in svnmucc as well.

* subversion/include/private/svn_subr_private.h
  (svn_config__get_default_config): New.

* subversion/libsvn_subr/config.c
  (svn_config__get_default_config): New.

* subversion/svn/svn.c
  (sub_main): Use svn_config__get_default_config, move hash get to just
   before use.

* subversion/svnmucc/svnmucc.c
  (sub_main): Use svn_config__get_default_config, move hash get to just
   before use.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1591015 13f79535-47bb-0310-9956-ffa450edef68