prep for nullary AM_INIT_AUTOMAKE

automake says:

  configure.ac:16: warning: AM_INIT_AUTOMAKE: two- and three-arguments forms are deprecated.  For more info, see:
  configure.ac:16: http://www.gnu.org/software/automake/manual/automake.html#Modernize-AM_005fINIT_005fAUTOMAKE-invocation

said manual (emphasis mine):

  AM_INIT_AUTOMAKE([OPTIONS])

    [...]

    This macro can also be called in another, deprecated form:
    AM_INIT_AUTOMAKE(PACKAGE, VERSION, [NO-DEFINE]). [...]
    vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
    However, differently from what happens for AC_INIT
    invocations, this AM_INIT_AUTOMAKE invocation supports shell
    variables’ expansions in the PACKAGE and VERSION arguments,
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    [...]

    If your configure.ac has:

      AC_INIT([src/foo.c])
      AM_INIT_AUTOMAKE([mumble], [1.5])

    you should modernize it as follows:

      AC_INIT([mumble], [1.5])
      AC_CONFIG_SRCDIR([src/foo.c])
      AM_INIT_AUTOMAKE

since AC_INIT(libstorage, $VERSION) wouldn't work, we nead to read
the VERSION file with m4; LIBVERSION is subject to the same
treatment, for symmetry.