Fixes failures in DR's handling of 32-bit rlimit system calls and in the client.file_io test: both need to use "struct rlimit64".
Adds proper syscall failure for hard limit > soft limit, and for raising the hard limit, along with tests of those cases. i#2980 covers allowing raising the hard limit for privileged processes.
Issue: #2950 (closed), #2980 Fixes #2950 (closed)