[Fix #310,#311] clojure-expected-ns with src/cljc

When the source path is src/clj{,c,s,x} instead of just src/
clojure-expected ns would create namespaces like clj.my-project.my-ns
whereas what's wanted is my-project.my-ns.

Reading boot.clj or project.clj to find out the user's src dirs is out
of scope for clojure-mode, so we use the simply heuristic that no
namespace should start with clj, cljc or cljs because these are the
idiomatic source directories in multi-source projects.

When improving clojure-expected-ns I extracted out two utilities,
clojure-project-dir and clojure-project-relative-path.  These
utilities already exist in clj-refactor so I opted to make them public
rather than private, as they are generally useful.

Author: expez

clojure-mode-util-test.el

@@ -0,0 +1,53 @@
+;;; clojure-mode-util-test.el --- Clojure Mode: util test suite  -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2014-2015 Bozhidar Batsov <[email protected]>
+
+;; This file is not part of GNU Emacs.
+
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; The unit test suite of Clojure Mode
+
+;;; Code:
+(require 'clojure-mode)
+(require 'cl-lib)
+(require 'ert)
+
+(let ((project-dir "/home/user/projects/my-project/")
+      (clj-file-path "/home/user/projects/my-project/src/clj/my_project/my_ns/my_file.clj")
+      (project-relative-clj-file-path "src/clj/my_project/my_ns/my_file.clj")
+      (clj-file-ns "my-project.my-ns.my-file"))
+
+  (ert-deftest project-relative-path ()
+    :tags '(utils)
+    (cl-letf (((symbol-function 'clojure-project-dir) (lambda () project-dir)))
+      (should (string= (clojure-project-relative-path clj-file-path)
+                       project-relative-clj-file-path))))
+
+  (ert-deftest expected-ns ()
+    :tags '(utils)
+    (cl-letf (((symbol-function 'clojure-project-relative-path)
+               (lambda (&optional current-buffer-file-name)
+                 project-relative-clj-file-path)))
+      (should (string= (clojure-expected-ns clj-file-path) clj-file-ns)))))
+
+(provide 'clojure-mode-util-test)
+
+;; Local Variables:
+;; indent-tabs-mode: nil
+;; End:
+
+;;; clojure-mode-util-test.el ends here