first phase of rework signalling for MP;
correction of error when coupling/uncoupling trains in explorer mode;
correction of error in explorer mode wrt detection of next signal;
correction of error when signal is situated immediately following speedlimit;
correction of error in dist_multi_sig_mr;
improvement in handling situation with two trains enabling same signal;
correction of error in TC state on removal of AI train;
correction of error when train runs through track loop.
git-svn-id: http://svn.uktrainsim.com/svn/openrails/trunk@1889 a9f3cfff-6c41-7446-b0ca-052bd761e6eb