special columns are processed. This will be documented.
Also some code cleanup and some changes to prepare the indexing of
nullable columns (not achieve yet)
modified:
storage/connect/colblk.cpp
storage/connect/colblk.h
storage/connect/connect.cc
storage/connect/connect.h
storage/connect/ha_connect.cc
storage/connect/ha_connect.h
storage/connect/macutil.cpp
storage/connect/mycat.cc
storage/connect/plgdbsem.h
storage/connect/reldef.cpp
storage/connect/reldef.h
storage/connect/table.cpp
storage/connect/tabmysql.cpp
storage/connect/tabmysql.h
storage/connect/tabodbc.h
storage/connect/tabtbl.cpp
storage/connect/tabutil.h
storage/connect/value.h
storage/connect/xindex.cpp
storage/connect/xindex.h
storage/connect/xtable.h
