Don't load module.la from current directory by default.

Don't load module.la from current directory by default.

* libltdl/ltdl.c (try_dlopen): Do not attempt to load an
unqualified module.la file from the current directory (by
default) since doing so is insecure and is not compliant with
the documentation.
* tests/testsuite.at: Qualify access to module.la file in
current directory so that test passes.