fix: error check for system("install"..)
add: create Singular/rlimit.{c,h} for setting resource limits
chg: raise RLIMIT_NPROC if necessary for fork()
fix: typo in messages of checklibs.c
Merge pull request #418 from steenpass/rlimit

raise RLIMIT_NPROC if necessary for fork()
fix: ring constructions with wrong coeffs (tr.517) + tests
port: freebsd needs uint64_t in rlimit.c