More graceful aborting from errors under mpi

[wshainin]

There's a pv_log but it's preprocessor directived to fprintf.

This is another to do listed in the TODO file that I'm moving here for better tracking.

[peteschultz]

The only place pv_log is used is in a file in the obsolete directory, so I removed its definition from pv_common.h 4ee6e44. The macros and functions that @riskybacon added in utils/PVLog.hpp are much more complete.

It would be good if pv_exit_failure called MPI_Finalize before exiting. I believe that that would require that all processes call pv_exit_failure, and currently it is often the case that only the process that fails calls exit(PV_FAILURE). It would also be preferable, for runs across multiple machines, if log messages could be sent from one process to another and printed there. This would require making sure that the root process regularly checked for messages from other processes.

[peteschultz]

The following preprocessor directives in pv_common.h are also unused:

#define LIF_STATS 1
#define MIRROR_BC_FLAG true
#define eventtype_t float
#define RAD_TO_DEG_x2 (2.0180.0/PI)
#define RAD_TO_DEG (180. / PI)
#define DEG_TO_RAD (PI/180.0)
#define MAX_CHANNELS 3
#define PHI0 0 // which phi buffer to use
#define PHI1 1 // which phi buffer to use
#define PHI_EXC 0 // which phi buffer to use
#define PHI_INH 1 // which phi buffer to use
#define PHI_INHB 2
#define RMIN 0.0
#define R2MAX (RMAXRMAX)
#define VEL (2.0RMAX)
#define RECV_FN void
#define PARAMS_FILE "params.txt"

I believe that all of these can be removed. Perhaps others that are used in the code could be made unnecessary as well.