Change C-c SPC to C-c j to avoid a conflict in org-mode

In org-mode C-c SPC is bound to `org-table-blank-field`
Bind ace-jump-mode to s-. as well
Mention guru-warn-only
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Use `completion-at-point` since `lisp-complete-symbol` is obsolete as of Emacs 24.4.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`lisp-complete-symbol` is obsolete
Merge remote-tracking branch 'upstream/master'