[rtmpdump] Build a shared library for librtmp

[Arne Morten Kvarving]

hi,

i'm currently working on integrating librtmp into xbmc
(http://www.xbmc.org) based on the patches from highlandsun.

since we're somewhat a high profile target, and want to cover our
arses, i'm writing it using a dlopen() approach to allow for drop-in
support. this means i need a shared library built, currently your
build system only builds a static one. from the looks of it the
easiest spot to add this is in the rtmpdump/ directory, since we
already have the defines for the lib deps etc. however, it feels kinda
bad. how should i proceed? i have a simple patch to do it in the
rtmpdump dir, but feels wrong..

spiff