initialization: use getrlimit(2)/setrlimit(2) to enable core dumps instead of exec(2).

using exec(2) is potentially insecure, as it depends on an outside utility.  the most robust way
to enable core dumps is to set the resource limits inside the program.
Merge pull request #12 from kaniini/master

initialization: use getrlimit(2)/setrlimit(2) to enable core dumps