fixup tests

Test was calling the wrong function in place of to_double. Also
fix up an answer value after this.

Fixes up commit 7cd205832f34098375aff05e34a12c37f16046d5
Merge branch 'master' of git://github.com/wesnoth/wesnoth

This partially reverts mordante's change to drop abs
rather than correct the expected result of expression.

Conflicts:
	src/tests/test_config.cpp