Minor enhancement to be able to enumerate table columns and dump table

entries also if the database name is not provided by using the current
database on MySQL and MSSQL, the 'public' scheme on PostgreSQL and the
'USERS' TABLESPACE_NAME on Oracle.
Minor bug fix so that when the user provide as SELECT statement to be
processed an asterisk, now it also work if in the FROM there is no
database name specified.
Minor layout adjustments.