Data on IE versions affected by \9 hacks might be wrong

[cvrebert]

In

bootstrap/scss/_custom-forms.scss

Line 130 in 726525c

// Includes IE9-specific hacks (noted by ` \9`).

among other places, it's claimed that (ignoring IE<=8 since we don't support them) the \9 hack only affects IE9. Recent testing calls this into question, claiming the correct compatibility situation is:

.selector { property: value \9; } // IE 6-8
.selector { property: value\9; } // IE 6-10

Note that this introduces the further wrinkle that whitespace affects the effect of the hack, which has minification implications.
Also note that the browserhacks.com site has bitrotted and isn't fully reliable anymore; see 4ae9b8/browserhacks#39 (comment)