log, vendor: vendor in log15 inline into our codebase

log/handler_go14.go

@@ -0,0 +1,23 @@
+// +build go1.4
+
+package log
+
+import "sync/atomic"
+
+// swapHandler wraps another handler that may be swapped out
+// dynamically at runtime in a thread-safe fashion.
+type swapHandler struct {
+	handler atomic.Value
+}
+
+func (h *swapHandler) Log(r *Record) error {
+	return (*h.handler.Load().(*Handler)).Log(r)
+}
+
+func (h *swapHandler) Swap(newHandler Handler) {
+	h.handler.Store(&newHandler)
+}
+
+func (h *swapHandler) Get() Handler {
+	return *h.handler.Load().(*Handler)
+}