Avoid using references to hold pointers

Using a reference to keep a smart pointer around is bad because doing so
prevents the reference-counting mechanism from working.  This should not
be an issue in the remaining cases fixed here, but a different instance
fixed in the parent commit caused issues with the previous fix itself.
Better fix them all for consistency.

drivers/run_tests.cpp

@@ -169,7 +169,7 @@ start_test(scheduler::scheduler_handle& handle,
            const config::tree& user_config,
            drivers::run_tests::base_hooks& hooks)
 {
-    const model::test_program_ptr& test_program = match.first;
+    const model::test_program_ptr test_program = match.first;
     const std::string& test_case_name = match.second;
 
     hooks.got_test_case(*test_program, test_case_name);
@@ -289,7 +289,7 @@ drivers::run_tests::drive(const fs::path& kyuafile_path,
             optional< engine::scan_result > match = scanner.yield();
             if (!match)
                 break;
-            const model::test_program_ptr& test_program = match.get().first;
+            const model::test_program_ptr test_program = match.get().first;
             const std::string& test_case_name = match.get().second;
 
             const model::test_case& test_case = test_program->find(

engine/scheduler.cpp

@@ -221,7 +221,7 @@ struct test_exec_data : public exec_data {
     /// \param user_config_ User configuration passed to the test.
     test_exec_data(const model::test_program_ptr test_program_,
                    const std::string& test_case_name_,
-                   const std::shared_ptr< scheduler::interface >& interface_,
+                   const std::shared_ptr< scheduler::interface > interface_,
                    const config::tree& user_config_) :
         exec_data(test_program_, test_case_name_),
         interface(interface_), user_config(user_config_)

utils/format/containers.hpp

@@ -52,7 +52,7 @@ template< typename T1, typename T2 >
 std::ostream& operator<<(std::ostream&, const std::pair< T1, T2 >&);
 
 template< typename T >
-std::ostream& operator<<(std::ostream&, const std::shared_ptr< T >&);
+std::ostream& operator<<(std::ostream&, const std::shared_ptr< T >);
 
 template< typename T >
 std::ostream& operator<<(std::ostream&, const std::set< T >&);

utils/format/containers.ipp

@@ -80,7 +80,7 @@ std::operator<<(std::ostream& output, const std::pair< T1, T2 >& object)
 /// \return The output stream.
 template< typename T >
 std::ostream&
-std::operator<<(std::ostream& output, const std::shared_ptr< T >& object)
+std::operator<<(std::ostream& output, const std::shared_ptr< T > object)
 {
     if (object.get() == NULL) {
         output << "<NULL>";