* libltdl/m4/ltdl.m4: Bump serial as we are changing the

* libltdl/m4/ltdl.m4: Bump serial as we are changing the
interface.
(LT_CONFIG_LTDL_DIR): New macro to centralise setting the
subdirectory used for libltdl.
(LTDL_CONVENIENCE): Continue backwards compatibility support for
declaring the libltdl source subdirectory with an argument, but
defer to LT_CONFIG_LTDL_DIR.
(AC_LIBLTDL_CONVENIENCE): Adjust to upgrade to the new style.
(LTDL_INSTALLABLE, AC_LIBLTDL_INSTALLABLE): Ditto.
(LTDL_INIT): lt_ltdl_dir is set by LT_CONFIG_LTDL_DIR now, and
even `./' needs trailing slashes trimming!  If the user didn't
upgrade their configure.ac yet, call LT_CONFIG_LTDL_DIR for them.
* libtoolize.m4sh (func_scan_files): If --ltdl option is given
without a directory argument, use the value from
LT_CONFIG_LTDL_DIR; if the argument is given, and there is also a
value in LT_CONFIG_LTDL_DIR, ensure they are the same.
* libltdl/configure.ac: Use it.
* NEWS: Updated.