Merge pull request cpp-netlib#645 from deanberris/fix/multiple-definition-swap

Fix multiple definition swap

Author: glynos

boost/network/utils/thread_pool.hpp

@@ -98,7 +98,8 @@ class thread_pool {
   sentinel_ptr sentinel_;
 };
 
-void swap(thread_pool &a, thread_pool &b) { a.swap(b); }
+inline void swap(thread_pool &a, thread_pool &b) { a.swap(b); }
+
 }  // namespace utils
 }  // namespace network
 }  // namespace boost