Install apm command when Atom starts

This changes the command installation to use symlinks instead
of copying over the contents of the file.

src/stdlib/fs-utils.coffee

@@ -73,8 +73,11 @@ module.exports =
     return done(false) unless path?.length > 0
     fs.exists path, (exists) ->
       if exists
-        fs.stat path, (err, stat) ->
-          done(stat?.isDirectory() ? false)
+        fs.stat path, (error, stat) ->
+          if error?
+            done(false)
+          else
+            done(stat.isDirectory())
       else
         done(false)
 
@@ -87,6 +90,13 @@ module.exports =
     catch e
       false
 
+  # Returns true if the specified path is exectuable.
+  isExecutable: (path) ->
+    try
+      (fs.statSync(path).mode & 0o777 & 1) isnt 0
+    catch e
+      false
+
   # Returns an array with all the names of files contained
   # in the directory path.
   list: (rootPath, extensions) ->