(svn r10928) [NewGRF_ports] -Add: An aircraft can only release the blocks on an airport that it actually owns.
This prevents accidentally allowing a race condition where one aircraft keeps releasing blocks that it ceased owning a while ago. It also gives FSM writers a little leeway that if they over-release too often, it doesnt damage the airport block status.

(svn r10925) [NewGRF_ports] -Add: Added graphics placement of Intercontinental and Helistation. State Machines not yet functional.
-Change: Both Intercontinental and Helistation now loaded for old games.
**All old game airports now have newgrf equivalents.**

(svn r10920) [NewGRF_ports] -Cleanup: remove the tables/files that were used to define airports as they will all be defined in a NewGRF and we do not need them anymore.

(svn r10919) [NewGRF_ports] -Codechange: use the dummy airport from the NewGRF instead of the hardcoded one.

(svn r10918) [NewGRF_ports] -Fix: do not mark NewGRF properties as "unknown"/"unhandled" when you have handled them correctly during load.

(svn r10917) [NewGRF_ports] -Fix: if you force NewGRFs to be always loaded, make sure it still forces the NewGRF to be loaded when it is marked as "init only".

(svn r10916) [NewGRF_ports] -Feature: Added Helidepot to HELI class in airportsextended.grf.

(svn r10915) [NewGRF_ports] -Fix: Recalculated MD5 of airports.grf to eliminate warning.

(svn r10914) [NewGRF_ports] -Fix: Dummy state machine positions modified.

(svn r10913) [NewGRF_ports] -Fix: Dummy state machine should be available to all aircraft, rather than none.