initialize err to 0
Add UNUSED declarations

Attribute added to function arguments that are not used, in order to suppres
"-Wunused-argument" warnings. UNUSED and UNUSED_IFNOTMPI are defined to
"__argument__((unused))__" if appropriate. The unused arguments are for
generic prototypes that are not used in specific implementations.
change main(argc, argv) to main(void) to avoid -Wunused-variable warnings
initialize com_model to NULL

allows program to abort safely
make inline initializations
set CFLAGS to '-std=c99 -O2 -g -Wall -Wextra'