(fixed) Bug: AI units stand around and do nothing in some scenarios

[softcoder]

RealtimeFreak pointed out the scenario where AI players would have some units standing around doing nothing. I made a fix in SVN (not included in beta3) that ignores resources that a unit cannot harvest. I have used RealtimeFreaks test mod to test this change and it seems to work properly now. Anyone who builds from SVN should be CAREFUL not to mix this change with rev 1035 (beta3) since it is NOT backwards compatible with beta3 since the AI logic is lightly different to fix this bug.