- 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.boost

@@ -0,0 +1,11 @@
+For your convenience and allowed by Boost's license terms, a subset of
+Boost is bundled with SimGear in $(top_srcdir)/src-libs/.
+
+Boost must be installed before you can build SimGear.
+
+Once Boost is installed you can return to configuring and building
+Simgear.
+
+This subset of Boost is taken from the current release, 1.27.0.
+
+Up to date Boost documentation is available at http://www.boost.org