PROXY table base on another table. Used by several other types.
  XCOL  proxy on a table having a colummn containing a list of values
  OCCUR proxy on a table having several columns containing the same type
        of values that can be put in a unique column and several rows.
  TBL   Not new but now internally using the PROXY table class.
- Fix 2 bugs in add_field:
        Change '=' to ' ' after the COMMENT keyword.
        Quote column names between '`' in the SQL string.
- Update xml test result to the CONNECT version

added:
  storage/connect/taboccur.cpp
  storage/connect/taboccur.h
  storage/connect/tabutil.cpp
  storage/connect/tabutil.h
  storage/connect/tabxcl.cpp
  storage/connect/tabxcl.h
modified:
  storage/connect/CMakeLists.txt
  storage/connect/ha_connect.cc
  storage/connect/ha_connect.h
  storage/connect/mycat.cc
  storage/connect/myconn.cpp
  storage/connect/mysql-test/connect/r/xml.result
  storage/connect/plgdbsem.h
  storage/connect/tabmysql.cpp
  storage/connect/tabtbl.cpp
  storage/connect/tabtbl.h
  storage/connect/valblk.cpp
  storage/connect/valblk.h