Remove unnecessary error handling

With the `auto_reconnect` option, `riakc_pb_socket:start_link/3` will
never return an error tuple.
Fix more dialyzer errors

Some of these were fixed by changing ignores in the
`dialyzer.ignore-warnings` file. Others were minor code changes dialyzer
illuminated. There are 5 warnings I didn't feel comfortable hiding:

```
riak_cs_app.erl:87: Function will never be called
riak_cs_config.erl:183: Function will never be called
riak_cs_gc_d.erl:381: Function will never be called
riak_cs_gc_d.erl:507: Function will never be called
riak_cs_storage_d.erl:360: Function will never be called
```

Each of these were ones I did not understand the exact cause.
Fix dtrace xref warning
Merge pull request #595 from basho/bugfix/wrd-dialyzer-fixups-01

Dialyzer/Xref cleanup