Only auto-load .cson and .json keymap files

This now prevents files such as .DS_Store from being loaded as a
keymap where previously all paths were loaded regardless of extension.

Closes #205

src/app/atom-package.coffee

@@ -26,15 +26,12 @@ class AtomPackage extends Package
       @metadata = fs.readObject(metadataPath)
 
   loadKeymaps: ->
-    for keymapPath in @getKeymapPaths()
-      keymap.load(keymapPath)
-
-  getKeymapPaths: ->
     if keymaps = @metadata?.keymaps
-      keymaps.map (relativePath) =>
+      keymaps = keymaps.map (relativePath) =>
         fs.resolve(@keymapsDirPath, relativePath, ['cson', 'json', ''])
+      keymap.load(keymapPath) for keymapPath in keymaps
     else
-      fs.list(@keymapsDirPath)
+      keymap.loadDirectory(@keymapsDirPath)
 
   loadStylesheets: ->
     for stylesheetPath in @getStylesheetPaths()

src/app/keymap.coffee

@@ -35,7 +35,7 @@ class Keymap
     @loadDirectory(fs.join(config.configDirPath, 'keymaps'))
 
   loadDirectory: (directoryPath) ->
-    @load(filePath) for filePath in fs.list(directoryPath)
+    @load(filePath) for filePath in fs.list(directoryPath, ['.cson', '.json'])
 
   load: (path) ->
     @add(fs.readObject(path))

src/stdlib/fs.coffee

@@ -59,11 +59,16 @@ module.exports =
 
   # Returns an array with all the names of files contained
   # in the directory path.
-  list: (rootPath) ->
+  list: (rootPath, extensions) ->
     paths = []
-    onPath = (path) =>
-      paths.push(@join(rootPath, path))
-      false
+    if extensions
+      onPath = (path) =>
+        paths.push(@join(rootPath, path)) if _.contains(extensions, @extension(path))
+        false
+    else
+      onPath = (path) =>
+        paths.push(@join(rootPath, path))
+        false
     @traverseTree(rootPath, onPath, onPath)
     paths