[rtmpdump] [PATCH] Fix Makefile for Darwin

[Scott D. Davilla]

>Current Makefile is broken on Darwin, first of all it does not 
>compile because its compiles as a bundle and not as a dynamic shared 
>library. Also the resulting library should be named 
>librtmpdump.0.dylib instead of librtmpdump.so.0. Attached patch 
>fixes these issues.

@hyc, these changes look fine to me and I can change XBMC's usage to 
use a dylib instead of a loadable bundle.