Move common functions copy_to_string and copy_from_string to new module graph_copy

Ghost User
2019-10-31T12:24:21+01:00

Multiple `import code from` for the same object file result in linker errors when `gcc` is used for linking. This MR moves the duplicate code between `dynamic_string` and `graph_copy_with_names` to a new module `graph_copy`. (We cannot import `dynamic_string` from `graph_copy_with_names`, because the former requires dynamics.)