upgrade to sbt 0.13.0-RC3

commenting out plugins as needed
sbt 0.13 upgrade: avoid deprecated sbt APIs
sbt 0.13: eliminate Build.scala using 0.13 features
sbt 0.13: cleanup using new macros

if not specifying the `test` scope on these breaks anything, I don't
know what it is. the new inputKey macro doesn't take scope arguments
like the old InputKey.apply did
sbt 0.13: minor cleanup using new macros
add comment
sbt 0.13: little syntax improvements
sbt 0.13: use new syntax in a few more places
Merge remote-tracking branch 'origin/headless' into sbt-0.13
upgrade to sbt 0.13.0-RC4
use latest models on sbt-0.13 branch
missing piece of sbt 0.13.0-RC4 upgrade
Merge remote-tracking branch 'origin/headless' into sbt-0.13
fix bin/shell.sh to work with sbt 0.13
Merge remote-tracking branch 'origin/headless' into sbt-0.13
Merge remote-tracking branch 'origin/headless' into sbt-0.13

Conflicts:
	project/JFlexRunner.scala
Merge branch 'headless' into sbt-0.13

Conflicts:
	bin/shell.sh
	project/ChecksumsAndPreviews.scala
	project/Depend.scala
Merge remote-tracking branch 'origin/headless' into sbt-0.13
upgrade to sbt 0.13.0-RC5
ENSIME is now available for sbt 0.13