src/sage/misc/gperftools.py: update for python3

C functions take bytes, not python strings. Without this, the profiler
tries to write to "/", fails, and proceeds to do very little.

Author: orlitzky

src/sage/misc/gperftools.py

@@ -162,7 +162,7 @@ def start(self):
         self._previous_sigprof_handler = self._libc().signal(SIGPROF, SIG_DFL)
         profiler = self._libprofiler()
         self._t_start = time.time()
-        rc = profiler.ProfilerStart(self.filename())
+        rc = profiler.ProfilerStart(str.encode(self.filename()))
         if rc < 0:
             raise ValueError('profiler failed to start')