* libltdl/Makefile.inc: New file, factored out of Makefile.am for

* libltdl/Makefile.inc: New file, factored out of Makefile.am for
use in non-recursive libltdl installations.
* bootstrap: Adjust.
* Makefile.am: include it.
(libltdl/Makefile.am): Adjust to build from the new
libltdl/Makefile.inc.
(SUBDIR_LIBOBJS): Renamed from this...
(LTDL_SUBDIR_LIBOBJS): ...to this.
* configure.ac: Adjust.
* doc/libtool.texi (Invoking libtoolize): Document the new modes
and libtoolize option to select them.
* libtoolize.m4sh: Parse new options, --nonrecursive, --recursive
and --subproject.  Install the appropriate files with --ltdl
according to the selected mode.
(func_scan_files): If --subproject, --recursive or --nonrecursive
options were not given, use the value from LT_CONFIG_LTDL_DIR; if
a mode was given, and there is also an argument to
LT_CONFIG_LTDL_DIR, ensure they are the same.
* NEWS: Updated.