Re-enable compileTimeOnly without breaking 2.10 support

Added a shim into the 2.10 build process in a annotation-shim directory.
Added a test (that needs an upgrade to compileTimeOnly to work) to verify that it fails as expected if the user forgets to add .call()

Downside: If someone else does the same trick there might be a conflict in the two sources

Signed-off-by: Ben Jackman <ben@jackman.biz>
Could we normalize `annotation-shim/` and `annotation-works/` to something like `scala-2.10/`?