respects locks. Before SMPng, one was able to call psignal()
using the "call" command, but this is no longer possible because it
does not respect locks by itself. This is very useful when one has
gotten their machine into a state where it is impossible to spawn
ps/kill or su to root.
In this case, respecting locks essentially means trying to aquire the
proc lock before calling psignal(). We can't block in the debugger,
so if trylock fails, the operation fails. This also means that we
can't use pfind(), since that will attempt to lock the process for us.
Reviewed by: jhb
da78f952f3