Meanwhile, database names with single quotes in names don't work very well

at all, and because of shell quoting rules this can't be fixed, so I put
in error messages to that end.

Also, calling create or drop database in a transaction block is not so
good either, because the file system mysteriously refuses to roll back rm
calls on transaction aborts. :) So I put in checks to see if a transaction
is in progress and signal an error.

Also I put the whole call in a transaction of its own to be able to roll
back changes to pg_database in case the file system operations fail.

The alternative location issues I posted recently were untouched, awaiting
the outcome of that discussion. Other than that, this should be much more
fool-proof now.

The docs I cleaned up as well.

Peter Eisentraut                  Sernanders väg 10:115