Add missing b2 testing module import.

example/Jamfile.v2

@@ -11,6 +11,8 @@
 # Boost Software License, Version 1.0. (See accompanying file
 # LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 
+import testing ;
+
 # this rule enumerates through all the sources and invokes
 # the run rule for each source, the result is a list of all
 # the run rules, which we can pass on to the test_suite rule: