heavily modified urrebot aiming code, and migrated some enemy handling

heavily modified urrebot aiming code, and migrated some enemy handling
code into aiming instead (not the cleanest organization, but more
efficient), this also means skills have changed, and their aiming is now
much smoother (now spectating them won't give you visual whiplash)
rewrote urrebot weapon selection code

git-svn-id: svn://svn.icculus.org/nexuiz/trunk@1109 f962a42d-fe04-0410-a3ab-8c8b0445ebaa