vim-patch:7.4.1407

Problem:    json_encode() does not handle NaN and inf properly. (David
            Barnett)
Solution:   For JSON turn them into "null".  For JS use "NaN" and "Infinity".
            Add isnan().
f1b6ac7229

src/nvim/eval.lua

@@ -190,6 +190,7 @@ return {
     invert={args=1},
     isdirectory={args=1},
     islocked={args=1},
+    isnan={args=1},
     id={args=1},
     items={args=1},
     jobclose={args={1, 2}, func="f_chanclose"},