[range] refactor use of examples in documentation to avoid redundancy

[SVN r82344]

doc/reference/adaptors/map_keys.qbk

@@ -18,31 +18,8 @@
 * [*Returned Range Category:] The range category of `rng`.
 
 [section:map_keys_example map_keys example]
-``
-#include <boost/range/adaptor/map.hpp>
-#include <boost/range/algorithm/copy.hpp>
-#include <boost/assign.hpp>
-#include <algorithm>
-#include <iostream>
-#include <map>
-#include <vector>
-
-int main(int argc, const char* argv[])
-{
-    using namespace boost::assign;
-    using namespace boost::adaptors;
-
-    std::map<int,int> input;
-    for (int i = 0; i < 10; ++i)
-        input.insert(std::make_pair(i, i * 10));
-
-    boost::copy(
-        input | map_keys,
-        std::ostream_iterator<int>(std::cout, ","));
-
-    return 0;
-}
-``
+[import ../../../test/adaptor_test/map_keys_example.cpp]
+[map_keys_example]
 [endsect]
 
 This would produce the output: