Fix ifdef for tr1 isnan.
Fix ifdef for tr1 isnan.

Not only can we not include it with Apple's gcc, we can't use it
either...


git-svn-id: 83c4c97093aeea62ac982fbfd516bf9db27f5c99@1341 c36c8488-0289-0348-9b64-b301f74bd9a7

BlueBrain/Tuvok,BlueBrain/Tuvok,BlueBrain/Tuvok