Enabled relative line numbers.

Currently done in a bit of a hacky way, I might try to turn it into a package at some point.

behavior.el

@@ -44,3 +44,15 @@
   (xterm-mouse-mode 1)
   (global-set-key [mouse-4] 'scroll-down-line)
   (global-set-key [mouse-5] 'scroll-up-line))
+
+;; Relative line numbers -- from: http://stackoverflow.com/a/6928112/42146
+(defvar my-linum-current-line-number 0)
+(setq linum-format 'my-linum-relative-line-numbers)
+(defun my-linum-relative-line-numbers (line-number)
+  (propertize
+   (number-to-string (abs (- line-number my-linum-current-line-number)))
+   'face 'linum))
+(defadvice linum-update (around my-linum-update)
+  (let ((my-linum-current-line-number (line-number-at-pos)))
+    ad-do-it))
+(ad-activate 'linum-update)