Backport aggregator stuff to 0.8

passes mima:

[tw-mbp-oscar algebird]$ ./sbt algebird-core/mima-report-binary-issues                                                                       
[info] Loading global plugins from /Users/oscar/.sbt/0.13/plugins
[info] Loading project definition from /Users/oscar/workspace/algebird/project
[info] Set current project to algebird (in build file:/Users/oscar/workspace/algebird/)
[info] Resolving com.googlecode.javaewah#JavaEWAH;0.6.6 ...
[info] algebird-core: found 0 potential binary incompatibilities
[success] Total time: 2 s, completed Dec 4, 2014 9:59:03 AM