BUG Move setting of log_active flag down

Previously, if there was an error opening the file (e.g., permission denied),
then the object would end up in a state where log_active was True, but there
was no logfile. The result was constant errors.

IPython/core/logger.py

@@ -69,8 +69,6 b' class Logger(object):'
             raise RuntimeError('Log file is already active: %s' %
                                self.logfname)
         
-        self.log_active = True
-
         # The parameters can override constructor defaults
         if logfname is not None: self.logfname = logfname
         if loghead is not None: self.loghead = loghead
@@ -124,6 +122,7 b' class Logger(object):'
             self.logfile.write(self.loghead)
 
         self.logfile.flush()
+        self.log_active = True
 
     def switch_log(self,val):
         """Switch logging on/off. val should be ONLY a boolean."""