TypeError fix on virtualenv init

stdout returns bytes, not string so I got TypeError on join on my machine
```
~> virtualenv venv                                                        
Traceback (most recent call last):
  File "/usr/bin/virtualenv", line 3, in <module>
    virtualenv.main()
  File "/usr/lib/python3.3/site-packages/virtualenv.py", line 821, in main
    symlink=options.symlink)
  File "/usr/lib/python3.3/site-packages/virtualenv.py", line 952, in create_environment
    home_dir, lib_dir, inc_dir, bin_dir = path_locations(home_dir)
  File "/usr/lib/python3.3/site-packages/virtualenv.py", line 1020, in path_locations
    inc_dir = join(home_dir, 'include', stdout.strip(), py_version + abiflags)
  File "/usr/lib/python3.3/posixpath.py", line 92, in join
    "components.") from None
TypeError: Can't mix strings and bytes in path components. 
```