Using pathlib in code to simplify the code

[lowks]

Using pathlib in code to simplify the code. This is an okay lib to add as it's already accepted into Python-3.4 mainline, so later we don't really have to do any changes to migrate to it.

[lowks]

There is actually one more to this that I have not finished yet...

28def walktree(dirname, callback):                                                                                                    
29    '''recursively descend the directory tree rooted at top,                                                                        
30       calling the callback function for each regular file'''                                                                       
31                                                                                                                                    
32    for f in os.listdir(dirname):                                                                                                   
33        pathname = os.path.join(dirname, f)                                                                                         
34        mode = os.stat(pathname).st_mode                                                                                            
35        if stat.S_ISDIR(mode):                                                                                                      
36            # It's a directory, recurse into it                                                                                     
37            walktree(pathname, callback)                                                                                            
38        elif stat.S_ISREG(mode):                                                                                                    
39            # It's a file, call the callback function                                                                               
40            callback(pathname)                                                                                                      
41        else:                                                                                                                       
42            # Unknown file type, print a message                                                                                    
43            print 'Skipping %s' % pathname                                                                                          
44                                           

This one is a bit complicated, I am still looking at how to replace it.