- Added metal extractor (still needs work)

 - Added metal extractor (still needs work)
 - Added transparent effect to objects being built
 - Added Extractor menu
 - Added menu section to constants
 - Added beta engineer build menu as class special ability (impulse 20)
 - th_die function is executed when a non-player object "dies". If the object has no th_die value, the function is ignored.
 - Added th_use .void. This is the function that gets executed when that object is activated by someone pressing the use key (extractor uses it)
 - Added Team:Nexuiz items:
  item_ctf_flag  - flag
  item_ctf_goal  - flag capture point (goal)

git-svn-id: svn://svn.icculus.org/nexuiz/trunk@878 f962a42d-fe04-0410-a3ab-8c8b0445ebaa