Allow tasks to be renabled on the fly via crtx
Better support for 0 rate in Spnl.

It's actually disabled now, instead of being only taking a really long time to run. (Long.MaxValue)
Test to verify the 0 rate feature and restart works
Merge pull request #43 from wajam/olivier-crtx-spnl

Support for 0 rate and restart in Spnl