Improve Boost.Python building.

* libs/python/build/Jamfile.v2: Sense the location of python headers. Export
  include paths.

* libs/python/example/Jamfile.v2: New file.

* new/targets.jam: Use refined properties for constructed
    dependency properties

* new/gcc.jam: Handle 'find-library'. Set soname for dynamic libraries.

* new/builtin.jam: New feature 'find-library'.


[SVN r15966]

Jamfile.v2

@@ -7,3 +7,6 @@ build-project libs/test/build ;
 build-project libs/date_time/build ;
 build-project libs/regex/build ;
 build-project libs/signals/build ;
+build-project libs/graph/build ;
+build-project libs/python/build ;
+

libs/python

@@ -1 +1 @@
-Subproject commit 037f9521369995702b6c611766572442de18c691
+Subproject commit 3cb4a029e06851bc8c7d38878e7a2b0c0d07f196

tools/build

@@ -1 +1 @@
-Subproject commit 6354355cbee737f270ea3fcb5736b88e5ba227b1
+Subproject commit d57002fce86c7ad8b1ad95cd21a25c980c576846