MCOL-529 Pool DBRM connections

DBRM connections are reused so that we don't have a huge amount of
TIME_WAIT sockets when there are large amounts of DML. Also applied to
i_s.columnstore_files

utils/messageqcpp/CMakeLists.txt

@@ -5,6 +5,7 @@ include_directories( ${ENGINE_COMMON_INCLUDES} )
 
 set(messageqcpp_LIB_SRCS
     messagequeue.cpp
+    messagequeuepool.cpp
     bytestream.cpp
     socketparms.cpp
     inetstreamsocket.cpp