take more care when applying default mysql.* inclusion filter

- The earlier fix to add --table=mysql.* was being
  unconditionally appended to the list of inclusion filters,
  and so by default would *only* extract the mysql.* tables
  (effectively excluding all other databases).  Now this is only
  included if at least one inclusion patterns matches so the
  specified table(s) and possibly mysql.* are included.
  This fixes issue #67
document change to -t/--table sandbox option
expand test_sandbox tests to load tables from a tarball
add simple upload script to contrib