Correct version_compare_condition_with_min() for the case where no minimum version is established by the version constraint. Add a simple test. Also fix test_feature_check_usage_subprojects by escaping regex metacharacters. if |condition| is '<', '<=' or '!=', the minimum version satisfying the condition is 0, so the minimum version for a feature is never met. if |condition| is '>=' or '==', the minimum version satisfying the condition is the version compared with, so the minimum version for a feature must be less than or equal to that. if |condition| is '>', the minimum version satisfying the condition is greater than the version compared with, so the minimum version for a feature must be less than that (it's this last condition that makes this function necessary, as in all other cases we could establish a definite minimum version which we could compare to see if it's less than or equal to the current version)