Fix an error in the type inference of bitstring data

Dialyzer was constraining bitstring data used in the construction of other
bitstring values too much. These constraints have now been relaxed.
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. :-)
Minor refactorings