Aw: Broken locking in old AddOnManager

> Hi there,
> 
> just to note it here, since I forgot to put it into the CVS change 
> message:
> 
> Both AddOnManager::RegisterReader()/Decoder() had a broken locking 
> strategy:
> 
> void
> AddOnManager::RegisterReader()
> {
> 	1) lock
> 		check if the reader already exists
> 	unlock
> 
> 	... initialize reader ...
> 
> 	2) lock
> 		add reader
> 	unlock
> }
> 
> When you lock again in 2), the same reader could have been added in the 
> meantime; you would have to check for its existence again.
> It's better in this case to hold the lock during the whole time, given 
> that the whole process is relatively light-weight.
> 
Well the idea was that RegisterReader() is only called from RegisterAddOns()
which is only executed once during startup (and only from a single thread).
The lock is only used to preserve list integrity (Rewind() changes internal list pointer).

As soon as we implement node watching to dynamically register/unregister plugins,
will get more complicated, but I still think this locking is ok.

Marcus