sbt: dirty hack to build 1.1.9 for 2.9

we still have at least one service running on scala 2.9. can't abandon
the older scala version yet. Unfortunately grizzled-slf4j doesn't have
a single version that supports both scala 2.9 and 2.10. 1.0.x supports
2.10 and 0.6.10 is the last version to support 2.9.

Rather than much around with making conditional version depenencies
right now, I'll commit this dirty hack. We'll at least cleanly build
build for the various 2.9 scala versions.