separate suppressOutput config out to the log obj

1: fix issues like this:
----------------------
when i add hooker to grunt.log.writeln function, but the verbose.writeln's supperssOutput config judge at the grunt.log.writeln.
so i got the grunt.verbose.writeln's  log message when i did'n want this;
example code : 
```
   hooker.hook(grunt.log, 'writeln', {
   	pre : function(){
   		console.log('grunt.log.writeln:' + arguments[0]);
   	}
   });
```
2: commit reset suppressOutput, as it don't change when the task run. i want to know why?