New plural rules for Scots Gaelic (gd)

MediaWiki (well, Siebrand, actually :-) imports the CLDR definitions, so your goal is to define the rules there. Have a look at the CLDR documentation Language Plural Rules and see what you can make of it. The 'mod' used at CLDR is equivalent to the use of '%' in the Firefox definition, i.e. the modulus of a number. You'll also need to qualify the different modes with a name, rather than a number.