Support for sbt 0.12

[jrudolph]

By:

• using the new sbt-cross-building for sbt 0.13 (currently only as SNAPSHOT version available)
• the new futures-backport library containing SIP-14 for Scala 2.9.2
• the new bintry for Scala 2.9.2 (which has yet to be published for this to work)
• a few changes to make the code compatible with sbt 0.12 / scala 2.9.2

This fixes #8.

In practice, there's a gotcha that bintray-sbt won't work together (java.lang.IncompatibleClassChangeError: Implementing class) with plugins depending on older dispatch versions which AFAIK for 2.9.2 means all plugins using dispatch because there's no 2.9.2 version of dispatch 0.11.0 because the futures-backport was previously missing from the picture.

Proof of concept: https://bintray.com/jrudolph/maven/sbt-dependency-graph

[softprops]

I'm just going to trust your changes and merge this :) I don't really have time to review right now but I don't want to hold you back. Proofs are enough for me!

[jsuereth]

@jrudolph You rock man. Thanks very very much for this! I'll test out shortly on my plugins.

[adriaanm]

FYI, @jsuereth, this causes the class change error when also using "com.typesafe.sbt" % "sbt-pgp" % "0.8" (on sbt 0.13.1 and 0.13.0)

[jsuereth]

@adriaanm do you mind opening up a full bug? Will have to fix sbt-pgp.

[softprops]

Do you guys still need the sbt 0.12.4 support? I'm thinking of doing a new release soon to fix some issues with ivy style publishes. I don't know how many projects are still using the the 0.12.4 line. At this point I hope we are at least encouraging ppl to make the leap to 0.13.(0,1,2) ect which I think should all be source compatible.

[adriaanm]

Sure, wasn't sure where the bug was. In general, it seems sbt could prevent plugins from depending on incompatible scala releases.

[jsuereth]

Yeah, 0.13.x is binary compatible, as is the 0.12.x series. However, we're still supporting 0.12 for another few months, at the least (until 1.0 is out). I think it's acceptable to support Previous 2 major, if possible. If it's just impossible, we may have to find an alternative solution.