build with ruby 2.2

[unak]

not tested running with ruby 2.2 yet. this patch only support to build.

[knu]

Oh, thanks.

I suppose a better fix would be s/\bConfig\b/RbConfig/g since even ruby 1.8 (which rsdl was originally written for) has RbConfig defined. Could you do that?

[Kagetsuki]

@knu I think @unak has a good solution here because it allows an easy override just-in-case. Think this can be pulled? It's a rather trivial fix and all - and as it is rsdl is kind of crippled.

[knu]

Closing this in favor of #6.