This is a first pass at Daniele's suggestion in Issue #8, although it is
definitely still buggy -- it is still possible for another transaction
to get in an AccessExclusive lock and perform DDL either before the
ACCESS SHARE lock is acquired or immediately after it is released.
Actually this leaves out the case of the SQL schema not consistent with the
library/binary installed, and this is a relatively likely case:
the user has run "make install" but the repack schema was already loaded
from an older version.
repack_all_database can return an error message: in case of any error different
from "missing schema" return the error and keep processing the other databases
instead of printing and stopping the program.
The output of the program is now something like:
$ pg_reorg --all
pg_reorg: reorg database "contrib_regression"
pg_reorg: reorg database "template1" ... skipped: pg_reorg is not installed in the database
