Maintaining backward compatibility in clone() signature

src/index.coffee

@@ -36,7 +36,10 @@ Git.init = (path, bare, callback) ->
 # callback   - Receives `(err, repo)`.
 #
 Git.clone = (repository, path, depth = 0, callback) ->
-  if (0 == depth)
+  if typeof depth is 'function'
+    callback = depth
+    depth = 0
+  if depth is 0 or typeof depth isnt 'number'
     bash = "git clone \"#{repository}\" \"#{path}\""
   else
     bash = "git clone \"#{repository}\" \"#{path}\" --depth \"#{depth}\""

test/index.test.coffee

@@ -44,6 +44,22 @@ describe "git", ->
     @timeout 30000
     repo = null
     newRepositoryDir = "#{__dirname}/fixtures/clone"
+    before (done) ->
+      git.clone "https://github.com/notatestuser/gift.git", newRepositoryDir, (err, _repo) ->
+        repo = _repo
+        done err
+    it "clone a repository", (done) ->
+      repo.should.be.an.instanceof Repo
+      repo.remote_list (err, remotes) ->
+        remotes.should.have.length 1
+        done()
+    after (done) ->
+      exec "rm -rf #{newRepositoryDir}", done
+
+  describe "clone() with depth", ->
+    @timeout 30000
+    repo = null
+    newRepositoryDir = "#{__dirname}/fixtures/clone_depth"
     before (done) ->
       git.clone "https://github.com/notatestuser/gift.git", newRepositoryDir, 1, (err, _repo) ->
         repo = _repo