log, vendor: vendor in log15 inline into our codebase

log/handler_go13.go

@@ -0,0 +1,26 @@
+// +build !go1.4
+
+package log
+
+import (
+	"sync/atomic"
+	"unsafe"
+)
+
+// swapHandler wraps another handler that may be swapped out
+// dynamically at runtime in a thread-safe fashion.
+type swapHandler struct {
+	handler unsafe.Pointer
+}
+
+func (h *swapHandler) Log(r *Record) error {
+	return h.Get().Log(r)
+}
+
+func (h *swapHandler) Get() Handler {
+	return *(*Handler)(atomic.LoadPointer(&h.handler))
+}
+
+func (h *swapHandler) Swap(newHandler Handler) {
+	atomic.StorePointer(&h.handler, unsafe.Pointer(&newHandler))
+}