devtools 1.4.1

• Fixed bug in wd() when path was ommitted. (#374)
• Fixed bug in dev_help() that prevented it from working when not using
  Rstudio.
• source_gist() respects new github policy by sending user agent
  (hadley/devtools)
• install_github() now takes repo names of the form
  [username/]repo[/subdir][@ref|#pull] -
  this is now the recommended form to specify username, subdir, ref and/or
  pull for install_github. (Thanks to Kirill Müller, #376)