JR40566 ODBC stage failing on custom update/insert SQL statements.

JR40566 reinstated the default behaviour of the ODBC stage as it was originally designed. 
However, to let the user to continue to use old job designs (not really supported) developed 
with a version of DS server code with a bug, a new env var DSODBC_EXECUTE_MULTI_STMTS_AS_ONE 
was added to allow the behaviour of e97866.