Make type equality comparison nominative
Make type equality comparison nominative

The C types system is nominative, meaning that two user-defined types
(struct, union, or enum) are equivalent if, and only if, their names
match. This patch makes the eris_typeinfo_equal() follow the same
convention.

Tangentially, this solves the issue of comparing opaque vs. non-opaque
pointers to user-defined types.

aperezdc/lua-eol,aperezdc/eris,aperezdc/lua-eol,aperezdc/eris