* cdemo/configure.in: renamed AM_PROG_LIBTOOL to AC_PROG_LIBTOOL

* cdemo/configure.in: renamed AM_PROG_LIBTOOL to AC_PROG_LIBTOOL
* demo/configure.in: likewise
* depdemo/configure.in: likewise
* libltdl/configure.in: likewise
* mdemo/configure.in: likewise
* libltdl/ltdl.c: in find_module() check whether libdir is defined,
  tryall_dlopen(): move deallocation of an already opened handle
  to lt_dlopen(), allocate the directory in lt_dlopen() dynamically,
  minor cleanups, fixed memory leak (name)
* libtool.m4: renamed all AM_ macros to AC_ and added aliases for
  compatibilty, updated AC_SYS_NM_PARSE (no undefined symbols,
  don't count the symbols)
* ltconfig.in: added thread_safe_flag_spec (not used yet),
  added generic variable for linker options "linkopts" in
  all archive_cmds
* ltmain.in: added -thread-safe flag (unused)