remaining phases of dfp-branch merge

[Ben Elliston]

I am now about half-way through the various phases I proposed for
merging the dfp-branch into mainline.  The patch I committed today was
quite big, so in light of David Edelsohn's note tonight, I will sit
back for a bit before dealing with the next chunk.

Here is what remains:

 * Merge in middle-end changes.
 * Merge in i?86 and powerpc64 backend changes.
 * Merge in the changes (incl. configury) to the runtime library.
 * Merge in the testsuite.

These phases are a bit smaller than the ones before them.  They will
be less invasive and quicker to review.

Ben