A test to ensure that the updated configuration properties support
correctly expands placeholders using mapped properties.

Prior to the updated support an `application.properties` file of the
form:

	my.prefix.some-url=http://github.com
	my.prefix.login-url=${my.prefix.some-url}/login

Would not correctly expand the placeholder against the environment
variable `MY_PREFIX_SOME_URL`

Closes gh-2496