#25 Change reaction to attempts to move neg mob items

[Geoff Cashman]

Currently, if you attempt to march, fly, nav, etc any
particular unit/ship/plane object, it will allow you to
conduct the entire command before letting you know
that the given object you are attempting to manipulate
does not have mobility.

Changing this would reduce some of the drudgery. It
would also allow a player to know upfront that a
particular movement/mission of a group of units would
potentially be different because of lack of mobility in
part of the set of things being moved.