Eliminate the RELOH2 relocation, as it never worked --- the address would be

Eliminate the RELOH2 relocation, as it never worked --- the address would be
calculated incorrectly because of overflow errors.

Replace it with an extended RELOPPC relocation which understands addis/ori
pairs; add an la pseudoop to the assembler which generates these and the
appropriate relocation. Make good.

--HG--
branch : dtrg-experimental-powerpc-branch