Pointer map for callbacks, make go1.6 happy
Pointer map for callbacks, make go1.6 happy

Go 1.6 does not allow us to pass go pointers into C that will be stored and¬
used in callbacks and suggests we use a value lookup for pointer callbacks.¬
https://github.com/golang/proposal/blob/master/design/12416-cgo-pointers.md¬

Fixes 'panic: runtime error: cgo argument has Go pointer to Go' in tests.

cocoonlife/goflac,cocoonlife/goflac