Make sbt --version respect SBT_OPTS and friends

[parched]

Having set SBT_OPTS="-Dsbt.boot.directory=/not/the/default" I found when I ran sbt --version SBT was being redownloaded into ~/.sbt. This fixes that and I assume SBT_OPTS wasn't ignored on purpose, but I'm not sure.

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[eed3si9n]

This fixes that and I assume SBT_OPTS wasn't ignored on purpose, but I'm not sure.

sbt/sbt-launcher-package#276 added it, and I'm guessing SBT_OPTS was ignored on purpose since mostly those define memory options.

[parched]

I'm guessing SBT_OPTS was ignored on purpose since mostly those define memory options.

Ok, I'm happy to close the PR if you think that's best? I worked around it by just doing sbt sbtVersion instead so not a blocker for me.

[eed3si9n]

I think the direction of the change is good but the tests are currently failing. It looks like the previous incantation didn't have color but the new one does?

[parched]

Ok, I've found the problem, will push a fix when I'm back at my computer.