Add example of calling Python modules from Boost.Build.

[SVN r34474]

v2/example/python_modules/python_helpers.py

@@ -0,0 +1,15 @@
+
+# Declare a couple of functions called from Boost.Build
+#
+# Each function will receive as many arguments as there ":"-separated
+# arguments in bjam call. Each argument is a list of strings.
+# As a special exception (aka bug), if no arguments are passed in bjam,
+# Python function will be passed a single empty list.
+#
+# All Python functions must return a list of strings, which may be empty.
+
+def test1(l):
+    return ["foo", "bar"]
+    
+def test2(l, l2):
+    return [l[0], l2[0]]