Enable machine specific handling of relocation section type, since amd64

Enable machine specific handling of relocation section type, since amd64
should use .rela.* instead of .rel.* sections, of type SHT_RELA instead
of SHT_REL.

* elf.h, elf.c: update calls to backend, passing relocations further in.
* elf-machine.h, elf-x86-amd64.c, elf-x86-x86.c: add support for setting
  relocation section name, type, and update amd64 to write RELA records.
  Also when creating a relocation and writing a value to the file, have
  it handled here to keep REL vs RELA distinctions hidden from elf.c.
* elf-rip.hex: update output to match new section type and data output.

svn path=/trunk/yasm/; revision=1160