Added nebu_absorb_shield shipstat

Added nebu_absorb_shield shipstat, as well as a prototype outfit, nebula_shielding0,
that uses it.  If a ship has nebu_absorb_shield, it will be applied to nebula damage
in the same way that dmg_absorb is applied to normal damage.  Removed nebula_dmg_shield,
nebula_dmg_armor, since they were presumably meant to do the same thing, but didn't
have any real code attached to them in the damage calcs.  The Thurion Integrity will
need to be updated, since it uses the old values, and since they didn't do anything,
I have no way of knowing what -80 and -97 were supposed to mean in that context.
I also added a nebu_absorb_armor shipstat as a placeholder, but it doesn't do anything
yet.
Merge remote-tracking branch 'upstream/master'
* Prevent scanning of systems that were already scanned in ec01.
Merge branch 'master' of https://github.com/BTAxis/naev
add a lua call to limit a pilots speed
* Moved Thurion ship gfx data into its proper location.
Merge branch 'master' of https://github.com/rkulhanek/naev
Bug#217 alternate fix
* Explanation of patch.
* Flintley event should work again.
refactor the lua call for limiting a ships maximum speed
cleanup some whitespaces
more cleanups
Reduce the speed of joannes ship to match the players ship. unless the player ship is to slow, then abort mission
Merge branch 'test-speedlimit' of https://github.com/toams/naev
change joannes route
Merge branch 'master' of https://github.com/toams/naev
Merge branch 'upstream/master'