It is set originally in reltool.config and ends up in the riak.rel file. The fact that your release still says 1.3.0rc2 is because of this line in reltool.config on master:

```erlang
{sys, [
       {lib_dirs, ["../deps", "../deps/riak_search/apps"]},
       {rel, "riak", "1.3.0rc2",
       %...
```