Estimate an upper bound on the number of particles to read into the cache and how many particles to loop over in DOPAIR2_VEC.

Force compiler to report shadowed variables. Removed all shadowed variables. Added the function scheduler_activate_send() to simplify the unskipping of MPI sends.

Changed call to part_is_active to new function. Also removed unnecessary load of v_hj in runner_doself2_vec.

Removed alternate version of doself2_vec that was slower than current version. Renamed some variables. Removed left-packing functions for force interactions as they are not used anymore.

Created new version of doself2_vec that computes force interaction on the fly, 2.1x faster than serial.

Corrected bug in last_pj calculation. Using the last active particle in the cell as the upper bound now works.

Fixed seg fault bug. Make sure that max_index_i[ci->count - 1] and max_index_j[0] are initialised to correct values when nothing is in range.