remove unused code in AgentSet classes

not just unused, but could be dangerous if used -- see comment removed
from ArrayAgentSet
remove debugging output
beef up StructureParserTests with some passing tests

adding them since they're going to fail once merged to master;
it's #414
Merge remote-tracking branch 'origin/5.0.x'

Conflicts:
	src/test/org/nlogo/compiler/StructureParserTests.scala
	src/test/org/nlogo/headless/TreeAgentSetTests.scala
fix StructureParser regression (fixes #414)
fix broken links in User Manual
fix theoretical bug in new StructureParser

might affect error messages under some circumstances, not really sure
add passing ExpressionParser test showing existence of issue #417

I'll fix the bug and update the test case in a subsequent commit
fix ExpressionParser bug -- fixes #417
update comment in headless.Dump
update comment
remove debugging output
as far as we know, NetLogo works on Windows 8
slight wording change on downloads page
Keeping around some stuff in 'NetLogoLite' for the Web Image extension
Merge branch 'topic' into 5.0.x
remove nulling out
Merge pull request #401 from NetLogo/remove-unused-agentset-methods

remove unused code in AgentSet classes
make `file-open` dictionary entry mention multiple open files
upgrade to ScalaTest 2.0.M6

I forget why I got the master branch on the ScalaTest 2.0 milestone/RC
upgrade train in the first place, but nonetheless, now that we're on
it, I feel responsible that we should stay on it until we have arrived
at a stable 2.0 release

(some good news is, I've been using 2.0 milestones and snapshots on
the headless branch witp no real problems)

changes needed to get compiling/running again:
- FunSuite is now a class not a trait, so I had to adjust the
  "extends" clause of some of our test stuff, and make a few of our
  classes into traits
- due to deprecation, renamed expectResult -> assertResult everywhere
- fixed a mistaken return type for a use of withFixture