Add option to prevent unexpected new column creation from table variables in concatenate.

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After running this script dt3 will contain a column 'a'. When using concatenate in a script this can result in unexpected behavior or the need to manually remove variables that are not used in the table. (Example: the 'SQL' table variable automatically added to tables returned from SQL Queries.) Provide an option in Concatenate() to rename duplicate table variables before concatenation if they would result in a new column. 

Names default to here(1);

dt1 = New Table( "Test", Add Rows(1), New Table Variable( "a", 1 ) );
dt2 = New Table( "Test", Add Rows(1), New Table Variable( "a", 2 ) );

dt3 = dt1 << Concatenate( dt2 );