Use std::isnan instead of isnan in rgb and rgba.h

[doctormo]

Fix issue #52 for popey. Use std::isnan instead of just isnan, std was already used in pxr/usd/lib/usd/timeCode.h so it should be fine.

[sunyab]

Hi @doctormo, just to update you on this, our current plan is to simply remove gf/rgb.h and rgba.h from the distribution since they're not being used. I'll leave this open until that actually goes through.

Also, just wanted to ask you to fill out the CLA per the instructions below should you wind up contributing more changes in the future: http://graphics.pixar.com/usd/docs/Contributing-to-USD.html

Thanks!

[doctormo]

Good to hear. Thanks for the update. No need to merge or anything.

We do a Public Domain declaration, since CLAs cause more paperwork and messing about than a normal multi-stakeholder open source project. So probably no large contributions, but the odd patch is easy enough to PD and hopefully is enough for your lawyers.

[sunyab]

Commit 57d4d15 was pushed last week, closing this out per my comment above. Thanks again!