with PostMessage() in case the message queue is full.
Some notes:
* for synchronous replies, we don't use this mechanism yet, but it could be
extended to do that as well.
* the code looks so complicated because we need a way to access the looper's
queue without locking it (to prevent deadlocks); like Dano's solution, I've
abused BTokenSpace to store a BDirectMessageTarget with a BHandler.
* we also need to decouple the lifetime of a looper's queue from its target,
as we cannot lock the looper, and therefore, can't guarantee it stays valid
as long as we're accessing it outside of BLooper.
* init_clipboard() now needs to be done after the global constructors have
been called - since sending messages now needs gDefaultTokens to be initialized.
Since this is done per image, it shouldn't cause any troubles, though.
* some minor cleanup, removed unused _msg_cache_cleanup_() and friends.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@19968 a95241bf-73f2-0310-859d-f6bbb57e9c96
