base: Reimplement the DPRINTF mechanism in a Logger class

This patch adds a Logger class encapsulating dprintf.  This allows
variants of DPRINTF logging to be constructed and substituted in
place of the default behaviour.

The Logger provides a logMessage(when, name, format, ...) member
function like Trace::dprintf and a getOstream member function to
use a raw ostream for logging.

A class OstreamLogger is provided which generates the customary
debugging output with Trace::OstreamLogger::logMessage being the
old Trace::dprintf.

src/python/swig/trace.i

@@ -33,17 +33,25 @@
 %{
 #include "base/trace.hh"
 #include "base/types.hh"
+#include "base/output.hh"
 
 inline void
 output(const char *filename)
 {
-    Trace::setOutput(filename);
+    std::ostream *file_stream = simout.find(filename);
+
+    if (!file_stream)
+        file_stream = simout.create(filename);
+
+    Trace::setDebugLogger(new Trace::OstreamLogger(*file_stream));
 }
 
 inline void
 ignore(const char *expr)
 {
-    Trace::ignore.setExpression(expr);
+    ObjectMatch ignore(expr);
+
+    Trace::getDebugLogger()->setIgnore(ignore);
 }
 
 using Trace::enabled;