===================================================================
- Implement a first support of the ALTER TABLE command. This fixes MDEV-5440
  but does much more than only that. See the details of how ALTER is supported
  in the new documentation and also in MDEV-5440 comment.
  This is done principally by implementing for CONNECT the virtual function
  check_if_supported_inplace_alter.
modified:
  storage/connect/connect.cc
  storage/connect/global.h
  storage/connect/ha_connect.cc
  storage/connect/ha_connect.h
  storage/connect/mysql-test/connect/r/bin.result
  storage/connect/mysql-test/connect/r/csv.result
  storage/connect/mysql-test/connect/r/dbf.result
  storage/connect/mysql-test/connect/r/dir.result
  storage/connect/mysql-test/connect/r/fix.result
  storage/connect/mysql-test/connect/r/index.result
  storage/connect/mysql-test/connect/r/ini.result
  storage/connect/mysql-test/connect/r/occur.result
  storage/connect/mysql-test/connect/r/pivot.result
  storage/connect/mysql-test/connect/r/vec.result
  storage/connect/mysql-test/connect/t/dbf.test
  storage/connect/plugutil.c
  storage/connect/user_connect.cc

- Fixes the tabname/table_name issue for XML tables. Implement
  multiple files XML tables.
modified:
  storage/connect/tabxml.cpp
  storage/connect/tabxml.h

- Set to varchar(256) the fields of catalog tables stored
  as STRBLK's (had length 0 --> CHAR(1))
  Add the GetCharString function to the VALBLK class
modified:
  storage/connect/ha_connect.cc
  storage/connect/valblk.cpp
  storage/connect/valblk.h
  storage/connect/value.cpp

- Translate CONNECT error messages to system_charset
  to avoid truncation on not ASCII characters.
modified:
  storage/connect/ha_connect.cc

- Update version number
modified:
  storage/connect/ha_connect.cc
  storage/connect/mysql-test/connect/r/xml.result

- Move the TDBASE::data_charset body from xtable.h to table.cpp.
  (dont' remember why)
modified:
  storage/connect/table.cpp
  storage/connect/xtable.h

- Other modifications are to enhance the support of OEM tables.
  In particular, they can now provide column definition in dicovery.
modified:
  storage/connect/colblk.h
  storage/connect/global.h
  storage/connect/ha_connect.cc
  storage/connect/mycat.cc
  storage/connect/plgcnx.h
  storage/connect/plgdbsem.h
  storage/connect/xtable.h

- Or to add or modify tracing.
modified:
  storage/connect/filamtxt.cpp
  storage/connect/ha_connect.cc
  storage/connect/plgdbutl.cpp
  storage/connect/tabfix.cpp
  storage/connect/tabmysql.cpp