Consider whether support for any RDBMS can be dropped

[dieggsy]

Not sure about this, since it would be nice to maintain as much backwards compatibility as possible. However:

• I wonder if anyone's actually using some of these. For example:
  • Is there any benefit to sqlite over sqlite3? Is it still used?
  • Do we really need clsql-postgresql-socket and clsql-postgresql-socket3?
• Less code makes this library easier to maintain and manage going forward.

[dieggsy]

I'll note that the last release of sqlite2 was in 2005.

[dieggsy]

It seems safe to drop SQLite2 - it's not even downloadable from sqlite.org