tests: avoid a failure due to m4 builtin 'sinclude' in package name

tests: avoid a failure due to m4 builtin 'sinclude' in package name

Even with Autoconf 2.69, AC_INIT is not very robust when to package
names that contain some selected m4 builtins; for example:

    $ echo 'AC_INIT([sinclude], [1.0])' | autoconf -o/dev/null -
    stdin:1: warning: file `' included several times

    $ echo 'AC_INIT([dnl], [1.0])' | autoconf -o/dev/null -
    /usr/bin/m4:stdin:1: excess arguments to builtin `m4_define' ignored
    autom4te: /usr/bin/m4 failed with exit status: 1

Reference:
<http://lists.gnu.org/archive/html/bug-autoconf/2012-11/msg00005.html>

* t/aclocal-m4-sinclude.sh (configure.ac): Use 'm4sinclude' as package
name in the AC_INIT invocation, to avoid tickling the just-described
bug.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>