Install atom executable during window.startup()

Previously this was done during `rake install`.

Also default to `~/github/atom` as the default resource path
when no `--resource-path` argument is specified.  This argument
will now be required when running in dev mode if the repository
is not at the default location.

Closes #300

src/app/window.coffee

@@ -1,5 +1,6 @@
 fs = require 'fs'
 $ = require 'jquery'
+ChildProcess = require 'child-process'
 require 'jquery-extensions'
 require 'underscore-extensions'
 require 'space-pen-extensions'
@@ -39,6 +40,7 @@ window.setUpEnvironment = ->
 
 # This method is only called when opening a real application window
 window.startup = ->
+  installAtomCommand('/opt/github/bin/atom')
   handleWindowEvents()
   config.load()
   atom.loadTextPackage()
@@ -65,6 +67,14 @@ window.shutdown = ->
   window.rootView = null
   window.project = null
 
+window.installAtomCommand = (commandPath) ->
+  return if fs.exists(commandPath)
+
+  bundledCommandPath = fs.resolve(window.resourcePath, 'atom.sh')
+  if bundledCommandPath?
+    fs.write(commandPath, fs.read(bundledCommandPath))
+    ChildProcess.exec("chmod u+x '#{commandPath}'")
+
 window.handleWindowEvents = ->
   $(window).on 'core:close', => window.close()
   $(window).command 'window:close', => window.close()