[2202] Don't use namespace std

Because of fear of possible future collisions.

src/lib/util/threads/lock.cc

@@ -23,7 +23,7 @@
 
 #include <pthread.h>
 
-using namespace std;
+using std::auto_ptr;
 
 namespace isc {
 namespace util {

src/lib/util/threads/tests/lock_unittest.cc

@@ -19,7 +19,6 @@
 
 #include <boost/bind.hpp>
 
-using namespace std;
 using namespace isc::util::thread;
 
 namespace {

src/lib/util/threads/thread.cc

@@ -22,7 +22,9 @@
 
 #include <pthread.h>
 
-using namespace std;
+using std::string;
+using std::exception;
+using std::auto_ptr;
 
 namespace isc {
 namespace util {