std.conv.to can't convert to bool?

[Andrej Mitrovic]

Wow not a minute later and I get bitten by my own solution. A C
function returned 1 for a supported feature, and -1 otherwise. And of
course -1 got converted to true, so then I had a bug in my code.

Damn silly C functions which return -1 when they should return 0.

Or damn me for not RTFM'ing.