If one item's name already exists in this OPEN TYPE, simply do not
add it to expression open_type_choice.

It slightly modifies previous commit :
dcc822a0.

With this modification, asn1f_parameterization_fork() will fork
parameterization if rhs_pspecs and stored rhs_pspecs have different
constraints, e.g. expressions parameterized by different
VALUESET references. Associated information object tables will be
generated accordingly.

This file can be included and transformed via automake

The generated Makefile.am.example is not really in the automake style.
Renaming it to converter-example.mk to reflect that it is a plain makefile
snippet and that it is for creating the converter-example

Ref :

https://github.com/vlm/asn1c/pull/237#issuecomment-342356046