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/command-installer.coffee

@@ -0,0 +1,50 @@
+path = require 'path'
+fs = require 'fs'
+_ = require 'underscore'
+async = require 'async'
+mkdirp = require 'mkdirp'
+fsUtils = require 'fs-utils'
+
+symlinkCommand = (sourcePath, destinationPath, callback) ->
+  mkdirp fsUtils.directory(destinationPath), (error) ->
+    if error?
+      callback(error)
+    else
+      fs.symlink sourcePath, destinationPath, (error) ->
+        if error?
+          callback(error)
+        else
+          fs.chmod(destinationPath, 0o755, callback)
+
+unlinkCommand = (destinationPath, callback) ->
+  fs.exists destinationPath, (exists) ->
+    if exists
+      fs.unlink(destinationPath, callback)
+    else
+      callback()
+
+module.exports =
+  findInstallDirectory: (callback) ->
+    directories = ['/opt/boxen','/opt/github','/usr/local']
+    async.detect(directories, fsUtils.isDirectoryAsync, callback)
+
+  install: (commandPath, commandName, callback) ->
+    if not commandName? or _.isFunction(commandName)
+      callback = commandName
+      commandName = path.basename(commandPath, path.extname(commandPath))
+
+    installCallback = (error) ->
+      if error?
+        console.warn "Failed to install `#{commandName}` binary", error
+      callback?(error)
+
+    @findInstallDirectory (directory) ->
+      if directory?
+        destinationPath = path.join(directory, 'bin', commandName)
+        unlinkCommand destinationPath, (error) ->
+          if error?
+            installCallback(error)
+          else
+            symlinkCommand(commandPath, destinationPath, installCallback)
+      else
+        installCallback(new Error("No destination directory exists to install"))

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) ->