Ripe Mango

Bug fixes/tweaks:

• fix current exchange test
• use non-relativistic GCA equations by default as they are more stable
• make TestPrtcl initialization always fallback to minimum number of particles if stride division under/overflows
• added missing twoD bindings for rGCA pusher
• fallback to using c style casts in bindings because of intel compiler
• fix end of non-void function in particle container set/get methods