[Radar] Move avatar age block into processProperties as this is more logical
[Radar] Remove duplicate code from updateAvatarList that was already performed during LLWorld::getAvatars
[Radar] Condense updateAvatarList to have less duplicate code
[Radar] Add a debug setting RadarRangeRadius to limit how far away avatars showing up on radar can be (0, the default, is unlimited)
[Radar] Remove unused member mDrawPosition
[Radar] Remove id null checks where null id is an impossibility due to earlier checks
[Radar] Switch from using frames in keeping track of ranges to using a bitset

Renames ALERT_TYPE_* to STAT_TYPE_* and ERadarAlertType to ERadarStatType
Removes mIn*Frame and accessors for these in favor of checking for the bit in mStats
Use mStats instead of mAgeAlert now.
Moves the range leave handling out of getAlive and into setPosition, where it logically belongs

Should fix Issue 43: Radar reports multiple times for agent entry upon rendering
[Radar] Fix up expireAvatarList to actually expire all the dead avatar entries, not just the back one.