A number of cosmetic and/or infrastructural changes.

A number of cosmetic and/or infrastructural changes.
Traffic Manager:
	* Just continue routing until we run out of flights. This change removes one of the major requirements for setting the "Home port" field.
	* Add a time restriction requirement for the aircraft scheduler; this became necessary after removing the limited-to-home-port routing restriction.
	* Added a new field to the heuristics calculation: take into account whether an aircraft has already been used in a previous session. Rotate aircraft assignments for greater variability across sessions.
	* Added a revision number to the cache files, so that old cache results, which are no longer compatible with the new file format, are discarded.

Groundnetwork and traffic control:
	* Added a revision number to the cache files, so that old and incompatible results are discarded.
	* The caching algorithm probably didn't store the correct data for airports that were processed while the user was quite far away. This is now corrected by checking whether the cached elevation data are equal to the generic airport elevation.
AIAircraft:
	* I've been searching for the infamous aircraft bend-over-backward bug, that can occur during initialization, but to no avail yet. The only variable potentially responsible (tgt_vs) wich can explain the irregular jumping behavior, as well as the weird pitch results is initialized in AIAircraft's only constructor (through AIBase), and I can't find any situation in the ground handling code where this variable could get bizarre values. But,
	* a couple of tgt_vs. calculations appear to be completely redundant. This value was calculated twice inside the ProcessFlightplan function, and subsequently again in the updateSecondaryTargetValues function. I have removed the calculations in the process flightplan function, without any apparent side effect.