consolidate append=true behavior of MySQL.load

[psteinb]

Thanks again for providing and supporting the library.

This is a a suggestion to avoid triggering a warning. If a user calls MySQL.load with append=true, I think she is likely to assume or know that the table under name already exists. Hence calling createtable to me doesn't make too much sense. For this, I suggest to put the entire try-catch clasue in the !append if statement.