Don't link Boost.Python to python library, and don't require

<threading>multi for embedding applications.

* libs/python/build/Jamfile.v2: (boost_python): Don't link
  to /python//python. Use /python//python_for_extensions.

* libs/python/test/Jamfile.v2: Remove <threading>multi project
  requirements.
  (py-run): Link to /python//python.
  (exec): Likewise.

* tools/build/v2/tools/python.jam: (pthread): Declare.
  (init-unix): Add 'pthread' to extra-libs.
  (


[SVN r34662]

libs/python

@@ -1 +1 @@
-Subproject commit 596e92404afee381fea635f694b734f2616b0d72
+Subproject commit a1e865061c2f80be160bc4d42f3c6edcac41df27

tools/build

@@ -1 +1 @@
-Subproject commit 762b3acc1e198740a19ef89f47e32bf082c18c07
+Subproject commit c89f6be0c4b8e2585978f893c5010043e7c00b09