build: more accurate dependencies on Boost libraries

See also named-data/ndn-cxx@5686c51b87b6a642aa2dc8d93e061caebbb226cc

Change-Id: I44f01b8dad76bf835d05f920a7943eeae3eb8c6f
diff --git a/examples/wscript b/examples/wscript
index 8f9faed..ad0cef9 100644
--- a/examples/wscript
+++ b/examples/wscript
@@ -3,11 +3,11 @@
 top = '..'
 
 def build(bld):
+    # List all .cpp files (whole example in one .cpp)
     for ex in bld.path.ant_glob('*.cpp'):
         name = ex.change_ext('').path_from(bld.path.get_bld())
-        bld.program(name='example-%s' % name,
+        bld.program(name=f'example-{name}',
                     target=name,
                     source=[ex],
                     use='NDN_CXX',
-                    includes='../src',
                     install_path=None)