These commands aren't used by config/default anyway, and
+default:multi-{next,previous}-line were moved to my private config.
Also fixes#1208 (:cd without args will now CD to $HOME).
These weren't reliable, often times buggy or overzealous about killing
buffers and processes. Best to do it manually or come up with a better
solution.
Should also fix void-function/void-variable errors caused by evil-magit
depending on the newer version of magit (#1174).
Also introduces a redesign of the SPC g prefix.
