MouseDownThread leaks a pthread+object

[ttcoder]

Picking up from ticket:12286#comment:11 ..etc

Seemingly not a huge biggie since this is a heap leak (not ports or thread_id's leak), and even then it's a couple KBytes on each mouse invokation.

Summary:

• depending on how the class is used elsewhere, the fix might be as simple as removing the kill_thread()/TRESPASS()/ASSERT() calls.
• if other users do not behave as BMenu does (e.g. they expect to delete the object themselves and cannot be easily re-organized) things are more dicey.. It might take a rewrite/reorganization of that class.

[pulkomandy]

Fixed in hrev49514, unfortunately the port leak is still there.

[ttcoder]

Thanks much pulkomandy! Let's test.. If there's no regression it will be the first time I've found an issue and a correct fix for it :-)