minor cleanup in test/headless.lang
use '/usr/bin/env scala' to start our auxiliary scala scripts

it's gotten annoying to maintain the 'bin/scala' script in the NetLogo
repo, so let's just stop. the original ideas behind that script were:
1) nobody had to install scala at the system level in order to do
   anything
2) the scripts always got the right version of Scala

now that we're using sbt not make to build, point 1 is already mostly
taken care of. so it no longer seems worth it to me to maintain the
'bin/scala' thing if it's only used by scripts that aren't essential
to the build.

as for point 2, changes in Scala have settled down a lot, so I'm
not especially worried that little-used scripts might break from
time to time. it seems like a bridge easily crossed when we come
to it.

a few other scripts, bin/profiles.scala, and bin/benches.scala,
are more complicated because they need NetLogo on the classpath.
I will handle them in separate commits.
latest from models repo
make bin/shell.sh use sbt to launch

I hadn't done it this way before because of JLine issues, but
I found a way to eliminate those.

the old way was hard to maintain because it had version number
and classpath stuff hardcoded into it, and it required `sbt package`
to be manually run first, which was easy to forget to do, and then
it either wouldn't work or you'd be running out of date code

the downside of going through sbt is increased startup time, but
oh well.
redo bin/{profiles,benches}.scala to run through sbt

sparing us manual classpath maintenance
get rid of bin/scala which is no longer used

the new way is to do everything through sbt
remove some unnecessary code in sbt build

it dawned on me that when we depend on "fullClasspath in Compile",
that triggers compilation, so an explicit additional dependency on
"compile in Compile" isn't necessary
Merge branch 'headless' into sbt-0.13

Conflicts:
	bin/shell.sh
	project/ChecksumsAndPreviews.scala
	project/Depend.scala