Don't export *log.Logger in Scanner

By introducing a lowercase type alias 'logger' for *log.Logger we can
now embed 'logger' in Scanner and not export it:

 % go doc Scanner
package symbolyze // import "."

type Scanner struct {
	// Has unexported fields.
}

GetRuntimeAddresses/symbolyze/symbolyze.go

@@ -28,7 +28,7 @@ type Scanner struct {
 	cache     map[string]uint64 // Contains (pathname, offset)
 	observers []Observer        // Callbacks
 
-	*log.Logger // Embedded logger
+	logger // Embedded logger
 
 	// Instead of using a boolean to indicate debugging, we use function
 	// members.  This way we can populate them with noop-functions in the
@@ -39,6 +39,10 @@ type Scanner struct {
 	err error // error state of the scanner.
 }
 
+// We use a lowercase type alias for *log.Logger so that we can embedd it in
+// Scanner without exporting it.
+type logger = *log.Logger
+
 // An Observer is a callback that can be registerd with Scanner.OnFound.  It
 // will be called with a pid and an offset.  Observers are called concurrently.
 // They have to be thread-safe.
@@ -54,7 +58,7 @@ func New(symbol, pathglob string) *Scanner {
 		pathglob: pathglob,
 		cache:    map[string]uint64{},
 
-		Logger: log.New(os.Stderr, "[symbolyze] ", log.Ltime|log.Lmicroseconds),
+		logger: log.New(os.Stderr, "[symbolyze] ", log.Ltime|log.Lmicroseconds),
 
 		// debugging is off per default.
 		debugf:  func(string, ...interface{}) {},