Cache target dir
Don't clean before compiling
Incremental compiles working with preserved timestamps
Cache resolutions
Dead code
Fixed sbt bootstrap startup
Fix tests
`clean` compiles when $SBT_CLEAN=true
Couple more `clean` assertions
Merge pull request #54 from heroku/incremental

Incremental Compilation
`bin/compile` env file support
Only use env file if it exists.
use sourced export_env_dir
Merge pull request #57 from heroku/envdir-sourced

use sourced export_env_dir from heroku-buildpack-jvm-common
update clean compile test
Remove whitelist from export-env-dir
Merge pull request #58 from heroku/envdir-no-whitelist

Remove whitelist from export-env-dir
Use java executable from $PATH
Remove user-env-compile instructions
Merge pull request #62 from heroku/sbt-vendored-java

sbt should use java on PATH