Merge pull request #605 from peastman/master

Added a missing return statement
Rewrote findBlocksWithInteractions() in a way that is both faster and simpler.
Merge pull request #607 from peastman/master

Bug fix to addExtraParticles()
Merge pull request #608 from peastman/master

Fixed bug in CustomManyParticleForce that caused crash
Ported the new version of findBlocksWithInteractions() to OpenCL (not yet debugged)
Bug fixes
Improved performance of building neighbor list on AMD GPUs
Fixed bug on Intel GPUs
Cleaned up obsolete code
Merge pull request #609 from peastman/nb

Rewrote the neighbor list generation kernel to be simpler and (slightly) faster
Merge pull request #611 from peastman/master

Prevent nan in CPU platform when two excluded particles are exactly on top of each other