Make `popover-arrow-color` default to `popover-bg`
Make `popover-arrow-color` default to `popover-bg`

BS3 commits: fcf26d0ef6bc04aa5fb1fc26bee9142b9e1b2818

2947721120/todc-bootstrap,mozillo/todc-bootstrap,aaroncnhk/todc-bootstrap,ztx1491/todc-bootstrap,todc/todc-bootstrap,2947721120/googlebt4,up2vs/todc-bootstrap,todc/todc-bootstrap,todc/todc-bootstrap