Extract SQL-Engine basics from DBD::File

Hi developers,

during refactoring of DBD::File and new wishes (e.g. SQL_IDENTIFIER_CASE
from Martin Evans, getinfo() support, ...) and my own try of a pure-perl
DBD for system tables (DBD::Sys) I see many common code.

I would like to extract the common code into a base class DBD - maybe
named DBD::SQLPerl (placed SQL in from for private methods and attributes
naming - the should have the prefix "sql_").

I know at least two additional DBD's which could benefit from that:
- DBD::Google from Darren Chamberlain (I don't know if he is subscribed
   to [email protected])
- DBD::Sys from me

If there are more, it would be great to know about them.

Best regards,
Jens