$grant setting in WP_Role->add_cap() not stored

[ringmaster]

WP_Role->add_cap() accepts a $grant parameter with a default, but does not pass that default on to the functions that make the value permanent.

Line 87 should be:
$wp_roles->add_cap($this->name, $cap, $grant);

[ryan]

(In [2904]) Pass along grant state when saving cap. Props Owen. fixes #1702