This allows us to rename struct & struct members in the source code
without changing the file format.
This is useful because the code becomes increasingly confusing when
names such as oops, ipo & dupli aren't used anywhere except DNA headers.
dna_rename_defs.h is used to define renaming operations.
The renaming it's self will be done separately.
Currently only a single function was duplicated which isn't so bad,
this change is to allow DNA versioning code to be shared between
dna_genfile.c and makesdna.c.
