Test cases using common object (database,user,table,..) names could probably
destroy customer data, when connecting to an already running server.
This Changeset contains an auxiliary routine include/testdb_only.inc" which
should be sourced by tests doing such dangerous things.
The test case will get a "[skipped]" when the environment variable
USE_RUNNING_SERVER is not 0 .
The modified mysql-test-run.sh sets USE_RUNNING_SERVER to 0, when
the "mysql-test-run" starts its own server, aka there was no "--extern"
option.
