Add more search pathes for potential libdirs

Index: pluginlib/include/pluginlib/class_loader_imp.hpp
===================================================================
--- pluginlib.orig/include/pluginlib/class_loader_imp.hpp
+++ pluginlib/include/pluginlib/class_loader_imp.hpp
@@ -323,6 +323,12 @@ std::vector<std::string> ClassLoader<T>:
       boost::filesystem::path bin("bin");
       lib_paths.push_back((path / bin).string());
 #endif
+      boost::filesystem::path lib64("lib64");
+      lib_paths.push_back((path / lib64).string());
+      boost::filesystem::path lib32("lib32");
+      lib_paths.push_back((path / lib32).string());
+      boost::filesystem::path libx32("libx32");
+      lib_paths.push_back((path / libx32).string());
       boost::filesystem::path lib("lib");
       lib_paths.push_back((path / lib).string());
     }