Change default FileTree implementation
Change default FileTree implementation

I have noticed on linux that the file cache updates aren't fast enough
for ExternalHooks. Say you have project b that depends on project a.
With a clean build, if you run b/compile, the file cache may not yet see
the changes to *.class files generated by project a. There are multiple
ways to fix this:
* don't use the file cache for binary products
* use the analysis results to invalidate the cache
* switch over to my hypothetical replacement file system

In the meantime, we should stop spamming users by default.

sbt/sbt,sbt/sbt,mdedetrich/sbt,mdedetrich/sbt,mdedetrich/sbt,sbt/sbt,mdedetrich/sbt,xuwei-k/xsbt,mdedetrich/sbt,mdedetrich/sbt,xuwei-k/xsbt,xuwei-k/xsbt,sbt/sbt,mdedetrich/sbt,sbt/sbt,xuwei-k/xsbt,xuwei-k/xsbt,sbt/sbt,sbt/sbt