#18 unnecessary beginTransaction method in DatabaseImpl

[mayur_naik]

The method beginTransaction in DatabaseImpl seems
redundant at this point. Since there is no
corresponding closeTransaction method, it would
probably be consistent to eliminate beginTransaction
completely from DatabaseImpl as well as from Database
and DatabaseCore, and add the begin method to Database
and DatabaseCore instead. Another reason to eliminate
the beginTransaction method is that it unnecessarily
sychronizes on "this". The begin method already
synchronizes on "this".