Do a :redrawstatus after setting window statuslines

For some reason the statusline doesn't always get redrawn automatically
after setting the statusline property for a window, and running
:redrawstatus when a buffer or window is entered seems to resolve this
issue.

plugin/vim/powerline.vim

@@ -31,6 +31,7 @@ function! s:UpdateWindows()
 	for winnr in range(1, winnr('$'))
 		call setwinvar(winnr, '&statusline', '%!Powerline('. winnr .', '. (w:window_id == getwinvar(winnr, 'window_id')) .')')
 	endfor
+	redrawstatus
 endfunction
 
 augroup Powerline