Forward-port of #2303.
The checking code has bad run time characteristics and would need to be fixed
for large projects with deep task dependency chains.
The code in sbt.Execute has been in production for a long time so it seems safe
enough to drop the extra checks by default. To debug issues, you can set
`-Dsbt.execute.extrachecks=true` to revert to the old behavior.
Cherry-picked 84cba9669c from branch 0.13 to 1.0.x
Tested manually:
$ grep 'version.*:=' build.sbt
version := "0.13.10-SNAPSHOT",
$ git archive --prefix=sbt-0.13.10-SNAPSHOT/ -o ~/Desktop/sbt-0.13.10-SNAPSHOT.tgz HEAD
$ cd ~/Desktop
$ ls
sbt-0.13.10-SNAPSHOT.tgz
$ tar xfz sbt-0.13.10-SNAPSHOT.tgz
$ cd sbt-0.13.10-SNAPSHOT/
$ sbt info
[info] Loading global plugins from /Users/dnw/.dotfiles/.sbt/0.13/plugins
[info] Loading project definition from /Users/dnw/Desktop/sbt-0.13.10-SNAPSHOT/project
[info] Updating {file:/Users/dnw/Desktop/sbt-0.13.10-SNAPSHOT/project/}sbt-0-13-10-snapshot-build...
[info] Resolving org.fusesource.jansi#jansi;1.4 ...
[info] Done updating.
[warn] There may be incompatibilities among your library dependencies.
[warn] Here are some of the libraries that were evicted:
[warn] * com.typesafe.sbt:sbt-site:0.8.1 -> 0.8.2
[warn] Run 'evicted' to see detailed eviction warnings
[info] Compiling 12 Scala sources to /Users/dnw/Desktop/sbt-0.13.10-SNAPSHOT/project/target/scala-2.10/sbt-0.13/classes...
[info] This is sbt 0.13.9
[info] The current project is {file:/Users/dnw/Desktop/sbt-0.13.10-SNAPSHOT/}sbtRoot 0.13.10-SNAPSHOT
[info] The current project is built against Scala 2.10.6
[info] Available Plugins: sbt.plugins.IvyPlugin, sbt.plugins.JvmPlugin, sbt.plugins.CorePlugin...
[info] sbt, sbt plugins, and build definitions are using Scala 2.10.5
The compiler bridge had a dependency on the scala compiler in the
version defined in the build definition. This means that when trying to
fetch the compiler bridge for, say, Scala 2.9.2, we would also pull in
the Scala compiler 2.10.5.
The compiler bridge now has a "provided" dependency on the Scala
compiler.