Fix for issue #955

Enhancements to the lein repl task regarding the treatment of the initial namespace. The individual commits take care of the following, in that order:

1. evaluate the `:init` form before starting the server; remove the evaluation of the `:init` form from `:repl-options/:custom-init`;
2. add initial namespace to the list of `init-requires`; remove `require init-ns` from `:repl-options/:custom-init`;
3. bind (in userland context) `leiningen.repl.config/project-map` to the project map;
4. now that `require init-ns` happens before server startup, make the repl connection timeout longer (1 minute);
5. try to start the nrepl server even if some requires fail. This is to maintain the currently observed behavior where `require init-ns` is happening after the server has already started;
6. adapt the tests to the new code.

With these changes any nrepl client may evaluate

```clojure
(when-let [pm (resolve 'leiningen.repl.config/project-map)] 
  (in-ns (or (-> @pm :repl-options :init-ns) (:main @pm))))
```

to enter the initial namespace.