bug#18189: customized value of 'vc-annotate-background-mode' is applied only after restarting Emacs

[Glenn Morris]

Juri Linkov wrote:

> `vc-annotate-background-mode' is defined before `vc-annotate-color-map'
> in the source file vc-annotate.el, so there is a cyclic dependency
> in these variables.  When I tried to provide it directly in the `defcustom'

Usually that's a sign you need an :initialize as well as a :set, and/or
a :set-after.