Fix notification for duplicate modules

Dialyzer fails when asked to analyze multiple modules with the same name, but
the error message was erroneous. With this patch Dialyzer generates a correct
error message.

Bug reported and patch submitted by Maxim Treskin.
Fix minor error in natively compiled module list

Even though dialyzer_typesig is the module doing most of the work, compiling it
to native code twice will not make it faster than the rest. :-)