SQLite support / database portability for EnsEMBL

This is my portability work to date.
See docs/README.db_portability, and in particular the disclaimer therein :-)

I have verified as far as I can that the test suite still passes under MySQL.

Under SQLite:
* cliHelper.t is skipped - not supported yet
* dbEntries.t fails one test, I suspect this is down to the test rather than the code (autoincrement differences) but further checking required.
* schema.t and schemaPatches.t fail.

All the best
Michael