change all memory size variables to long ints
Darshan uses a couple of variables to track module memory footprints that involve int instead of long (or preferably size_t). I changed these to type long to harmonize with the existing static long darshan_mod_mem_quota in this MR, but should these all more properly be size_t? If so I can change.
The problem that triggered this was trying to build with --with-mod-mem=2048; GCC detected a possible overflow condition.