Right now uuid4 can be implemented one of 3 ways:

- If there's a libuuid (and it's not OS X's) it uses that.
- Fallback to os.urandom
- If that raises an exception, fall back to the random module

I propose to simplify this to _just_ use os.urandom always. Reasons:

- Its security properties are more obviously correct. (There's a large comment in uuid.py about how libuuid doees the wrong thing with fork on OS X, who knows if it's correct on other platforms)
- It's simpler.
- It's faster:

a_gaynor@miranda:~$ python -mtimeit -s "import uuid; import os; import ctypes" "_buffer = ctypes.create_string_buffer(16); uuid._uuid_generate_random(_buffer); bytes(_buffer.raw)"
100000 loops, best of 3: 10 usec per loop
a_gaynor@miranda:~$ python -mtimeit -s "import uuid; import os; import ctypes" "_buffer = ctypes.create_string_buffer(16); uuid._uuid_generate_random(_buffer); bytes(_buffer.raw)"
100000 loops, best of 3: 10.3 usec per loop
a_gaynor@miranda:~$ python -mtimeit -s "import uuid; import os; import ctypes" "_buffer = ctypes.create_string_buffer(16); uuid._uuid_generate_random(_buffer); bytes(_buffer.raw)"
100000 loops, best of 3: 9.99 usec per loop
a_gaynor@miranda:~$ python -mtimeit -s "import uuid; import os; import ctypes" "_buffer = ctypes.create_string_buffer(16); uuid._uuid_generate_random(_buffer); bytes(_buffer.raw)"
100000 loops, best of 3: 10.2 usec per loop
a_gaynor@miranda:~$ python -mtimeit -s "import uuid; import os; import ctypes" "_buffer = ctypes.create_string_buffer(16); uuid._uuid_generate_random(_buffer); bytes(_buffer.raw)"
100000 loops, best of 3: 10.2 usec per loop
a_gaynor@miranda:~$
a_gaynor@miranda:~$
a_gaynor@miranda:~$
a_gaynor@miranda:~$
a_gaynor@miranda:~$ python -mtimeit -s "import uuid; import os; import ctypes" "os.urandom(16)"
100000 loops, best of 3: 8.94 usec per loop
a_gaynor@miranda:~$ python -mtimeit -s "import uuid; import os; import ctypes" "os.urandom(16)"
100000 loops, best of 3: 8.92 usec per loop
a_gaynor@miranda:~$ python -mtimeit -s "import uuid; import os; import ctypes" "os.urandom(16)"
100000 loops, best of 3: 8.97 usec per loop
a_gaynor@miranda:~$ python -mtimeit -s "import uuid; import os; import ctypes" "os.urandom(16)"
100000 loops, best of 3: 8.93 usec per loop
a_gaynor@miranda:~$ python -mtimeit -s "import uuid; import os; import ctypes" "os.urandom(16)"
100000 loops, best of 3: 8.94 usec per loop
a_gaynor@miranda:~$
a_gaynor@miranda:~$
a_gaynor@miranda:~$ python --version
Python 2.7.3