[$] Modifying another process's system calls

The ptrace()system call allows a suitably privileged process to modify another in alarge number of ways. Among other things, ptrace() can interceptsystem calls and make changes to them, but such operations can be fiddlyand architecture-dependent. This patch series fromDmitry Levin seeks to improve that situation by adding a newptrace() operation to make changes to another process's systemcalls in an architecture-independent manner.