Only expand default function/macro when there is no platform-specific implementation. (from Hans Huebner)

Finished conversion from methods to functions with defaults (Stelian Ionescu <sionescu@common-lisp.net>)

Centralized loading and checking of impl-specific thread libraries (Stelian Ionescu <sionescu@common-lisp.net>)

Apparently a bad reversion while resolving some repo conflicts.

Added a file containing the MIT license and a copyright and license notice in
each source file

Exported *supports-threads-p* so that apps can check that variable.
Some other small changes to make it load and 'work' on clisp.