Check for object autoImport in auto plugins. Fixes #1314
Merge pull request #1318 from sbt/topic/1314

Check for object autoImport in auto plugins.
Updated on Changes.rst
Back out autogc fix to be optionally enabled.

Workaround for #1329
Modify changes with latest RC changes.
Merge pull request #1332 from sbt/wip/disable-force-gc

Default force gc to false
Fix pattern match on buildLoaders.

Fixes #1341