Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Separate out the ELF relocation code from the ELF loader, and add
better relocation support for the amd64 and i386 platforms. This
should not result in any change in functionality, but moves a step
towards supporting the relocatable object file modules on amd64.

The same hack/trick as load_elf*.c uses is used here to simultaneously
support both elf32 and elf64 on amd64 and i386.