New file naming

is implemented. Regression tests are passed.
make distclean + initdb are required.

Now all file/dir names are numeric. OIDs are used
for databases *and* relations on creation, but
relation file names may be changed later if required
(separate from oid pg_class.relfilenode field is used).

ALTER TABLE RENAME is rollback-able now. I think that
it's very easy to make DROP TABLE rollback-able too
(file should be removed after xaction committed) but
I have no time to deal with this currently.

There is still one issue - database locations. They don't
work at the moment. I'm going to use soft link for them.
Thomas, is it ok?

Vadim