John's fix for the minimize/close/maximize controls no longer working.

John's fix for the minimize/close/maximize controls no longer working.
WIN32 expected us to pass the message on up the chain (or do something
else with it), rather than just throwing away the event, for a certain
class of events.  (See the diffs for more details.)

The code is also slightly reformatted from what was previously in the
repository.

git-svn-id: svn+ssh://svn.code.sf.net/p/freeglut/code/trunk/freeglut/freeglut@334 7f0cb862-5218-0410-a997-914c9d46530a