Added a check for a '.' in the column name before prepending a table name to the...

Added a check for a '.' in the column name before prepending a table name to the column name to avoid incorrect TABLE.COLUMN names when using a FROM clause

SF PATCH#766404 - SetColNull() was not correctly setting CbValue = SQL_NULL_DATA so that NULL columns still appeared to have data in some cases

Cleaned up some internal variable naming conventions

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@22589 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775