a small Graphic-Forms fix that helps SLIME users

Folks that have downloaded the 0.7.0 release, and who want to use SBCL / SLIME to develop Graphic-Forms apps, should apply the following patch.

In src/uitoolkit/widgets/top-level.lisp edit the INITIALIZE-INSTANCE method such that the INIT-WINDOW call is followed by a call to SHOW

< (init-window self classname register-func owner text)))
---
> (init-window self classname register-func owner text)
> (show self nil)))

Then reload or recompile top-level.lisp and try starting some apps. For me, this alleviates the hanging problem that occurs when running GF apps on SBCL / SLIME.