The default is "false", allowing for regular default JNDI access e.g. in
JndiPropertySource. Switching this flag to true is an optimization
for scenarios where nothing is ever to be found for such JNDI fallback searches
to begin with, avoiding the repeated JNDI lookup overhead.
Note that this flag just affects JNDI fallback searches, not explicitly configured
JNDI lookups such as for a DataSource or some other environment resource.
The flag literally just affects code which attempts JNDI searches based on the
JndiLocatorDelegate.isDefaultJndiEnvironmentAvailable() check: in particular,
StandardServletEnvironment and StandardPortletEnvironment.