JDBC drivers: fix 'Unsupported URL' – drivers might be called witrh wrong URLs and then they should (according to the JavaDoc) return null instead of throwing an exception. This problem occurred when --test-connection was testing multiple connections in parallel.

# This code depends on make tool being used
DEPFILES=$(wildcard $(addsuffix .d, ${OBJECTFILES} ${TESTOBJECTFILES}))
ifneq (${DEPFILES},)
include ${DEPFILES}
endif