Allow Jedi to be imported from a REPL on Windows

Colorama and Pyreadline interfere on Windows, causing the mere act of importing Jedi from the Python prompt to cause a scrolling set of errors (see #364).  
This PR adds an `os.name` check to `debug.py`, allowing for `colorama` support on all other platforms, but avoiding the troublesome behavior on Windows.  I tested this on Windows 7 64 bit and Linux Mint 16 32 bit.