MXS-2015: Remove buffer iterator

The iterator to the buffer isn't really needed as the beginning of the
buffer can be used instead. This should make the code more robust. Changed
the internal buffer from a vector to a deque as the latter is more
appropriate for insertion on one end and consumption on the other.

connectors/cdc-connector/cdc_connector.h

@@ -21,6 +21,7 @@
 #include <string>
 #include <tr1/memory>
 #include <vector>
+#include <deque>
 #include <map>
 #include <algorithm>
 #include <jansson.h>
@@ -137,8 +138,7 @@ private:
     SValueVector m_keys;
     SValueVector m_types;
     int m_timeout;
-    std::vector<char> m_buffer;
-    std::vector<char>::iterator m_buf_ptr;
+    std::deque<char> m_buffer;
     SRow m_first_row;
     bool m_connected;