Replace the obsolete race check from GiveUnitCrateAction.
Fixed drop-zone units
Merge pull request #5974 from pchote/cratefix

Fix unit collection crates and drop-zone maps.
Adds the RequiresPrerequisites field into ProvidesCustomPrerequisite and all the logic behind it.
Fix aircraft losing selection outside the map borders

Fixes #5651
Merge pull request #5965 from WolfGaming/CustomPrereqChange

Adds the RequiresPrerequisites field into ProvidesCustomPrerequisite
Merge pull request #5967 from obrakmann/fix5651

Fix aircraft losing selection outside the map borders