Update prelude-lisp.el

Use `completion-at-point` since `lisp-complete-symbol` is obsolete as of Emacs 24.4.
Merge pull request #465 from bixuanzju/patch-1

`lisp-complete-symbol` is obsolete
Use ruby-mode for Podfile

A Podfile is used for CocoaPods to do a Bundler like dependency
management in XCode projects. Similar to a Rakefile or a Gemfile the
Podfile contains a dependency description in a Ruby based DSL.
Merge pull request #473 from jehrhardt/podfiles

Use ruby-mode for Podfile
Merge remote-tracking branch 'upstream/master'