Handle exit from Mix.Project.load_paths (instead of crashing node)

This handles the situation where reprise gets packaged into a release, where a call to Mix.Project.load_paths results in this error:
```
18:33:15.626 [error] GenServer Reprise terminating
Last message: :wake
State: {{{2014, 10, 31}, {18, 33, 14}}, 1000}
** (exit) an exception was raised:
    ** (Mix.Error) Cannot access build without an application name, please ensure you are in a directory with a mix.exs file and it defines an :app name under the project configuration
        (mix) lib/mix.ex:235: Mix.raise/1
        (mix) lib/mix/project.ex:303: Mix.Project.compile_path/1
        (mix) lib/mix/project.ex:343: Mix.Project.load_paths/1
        (reprise) lib/reprise.ex:129: Reprise.Runner.beams/0
        (reprise) lib/reprise.ex:144: Reprise.Runner.beam_modules/0
        (reprise) lib/reprise.ex:171: Reprise.Runner.go/2
        (reprise) lib/reprise.ex:81: Reprise.Server.handle_info/2
        (stdlib) gen_server.erl:599: :gen_server.handle_msg/5
```
Instead of crashing the node, it causes the reprise application to terminate.