Fix p_endcopy.
For p_endcopy to work correctly, it must be the name of the next element
in struct proc after the end of the copy region, not the name of the
last element in the copy region. Currently, the last element
(p_elf_flags) is not being copied.
This appears to have been broken in r285670 (I think it should have been
set to p_klist instead), and I perpetuated the bug in r313407. I only
noticed it when merging r313407 to stable/10.