precompile against 2.9.3 and 2.10.1
toString for Stamp types
Logger.Null that discards logged messages
Provided details of why external binaries are detected as modified in incremental compiler debug output.
temporary option to disable classpath lookup in incremental compiler. Ref #710
Put default conflict warnings at the debug level. Fixes #709.

This is at debug instead of disabled so as to be a minimal change
during a point release.  It is dropped to debug because the conflict warnings
don't work correctly, especially for the artifacts they were designed for,
sbt and Scala.  This is due to the overrides and excludes present in 0.12.x.

The other possible use of conflictWarning is for general libraries, but
in 0.13 that is better served by using a strict conflict manager.  Therefore,
0.13 should drop the warnings based on the evicted modules completely.
Docs: latest change summary for RC2