go-1.6 support

[sbinet]

hi,

testing github.com/rainycape/dl with go-1.6, I get:

$> go test -v ./...
--- FAIL: TestFunctions (0.00s)
panic: runtime error: cgo argument has Go pointer to Go pointer [recovered]
    panic: runtime error: cgo argument has Go pointer to Go pointer

[bendikro]

Try this: #10