Force selectMainClass to just pick the first discovered one

This gets rid of asking the user on stdin, which hangs forever
on Windows. It might mess up a project that configures
selectMainClass itself, but few are likely to do that.

We do this in the probe rather than writing out a shim file
because we really don't want to change this if someone is
using regular sbt on a terminal.
Merge pull request #44 from sbt/wip/havocp-override-select-main

Force selectMainClass to just pick the first discovered one
Fix nondeterministic sort that broke integration tests (nondeterministically)
Clean up sbt version cut-and-paste in integration tests

This could certainly be improved further (for example
by getting the versions from the build) but at least
with this further improvements will be more localized.
Merge pull request #45 from sbt/wip/havocp-version-cnp

Integration test fixes / cleanups
Merge remote-tracking branch 'origin/master' into wip/sbt-rc-formal-api