- Added src-libs/boost.tar.gz and README.boost. This is in anticipation

of actually using them in the flightgear event manager.
- Now that we have several add on libs we are bundling with simgear (but
  not automatically built as part of the simgear build) I have moved them
  to their own subdirectory (src-libs).

README.zlib

@@ -1,7 +1,7 @@
 For your convenience and allowed by zlib's license terms:
 http://www.gzip.org/zlib/zlib_license.html a copy of the zlib source
-is bundled with SimGear.  You must have zlib installed before you can
-build SimGear.
+is bundled with SimGear in $(top_srcdir)/src-libs/.  You must have
+zlib installed before you can build SimGear.
 
 - Most linux distributions have a zlib package.  For linux
   developers, we recommend ysou install your distributions package