added contrail effects to sniper shots
Merge pull request #4453 from Mailaender/sniper-contrails

Added contrail effects to sniper shots
fix client join/leave race with master server ping
Merge pull request #4461 from chrisforbes/master-ping-thread-safety

fixes #4459
Merge pull request #4464 from pchote/attackmove

Add AttackMove to C&C helicopters
Simplify HeliFly interface.
Add range support to HeliFly.
Simplify Fly interface.
Add range support to Fly.
Ensure that planes circle after being ordered via IMove.
Add Guard support to C&C helicopters.
Add MinRange plumbing to attack activities.
Add MoveAdjacentTo overload for moving within a range.
Use MoveAdjacentTo for attack activities.

Fixes #2104. Fixes #2923. Fixes #4455.
Adjacent cells may be blocked by actors, too.

Fixes #4449.
Don't cancel MoveAdjacentTo until the inner order has completed.
Update changelog.