one big messy commit for the status quo, forces sorts of the active cells in each step, does not use task_type_sub_*, and probably sorts some cells twice. but it works.

Check that the particles interacting in the SELF or PAIR tasks have been properly drifted to the current time

Added debugging checks to the pair and self tasks to make sure cells have been drifted to this point before they get updated.

Added debugging checks to the pair and self tasks to make sure cells have been drifted to this point before they get updated.

Check whether particles or cells are active via an inlined function rather than via a direct read of engine->ti_current

Replaced all calls to fminf and fmaxf by the macros that was added for the integer min/max functions.

Renamed 'h' in cell struct to 'width' and renamed 'h' and 'ih' in the space struct to 'width' and 'iwidth'.

No longer works so is just crufting up the code

functions. CPU_TPS is now only found in one Makefile.am and one
file, clocks.c.

Many of the uses are commented out or protected by TIMER_VERBOSE.
TIMER_VERBOSE no longer compiles, so these changes are untested
and just aim to guide the future...