Fix mantis 2905: lead sight for secondaries uses subsys distance when targeting a subsys

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@9998 387891d4-d844-0410-90c0-e4c51a9137d3
some updates to r9885 per discussion with Goober5000

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@9999 387891d4-d844-0410-90c0-e4c51a9137d3