Move mainline to autoconf 2.59

[Kelley Cook]

With a recent patch by Hans-Peter Nilsson, we have unexpectedly moved
to autoconf 2.58 (which in the FSF version doesn't compute absolute
path names correctly).

Separately, libstdc++ recently moved to autoconf 2.59 (along with
automake 1.8.2)

Both of these are contrary to documentation with says "autoconf 2.57
(exactly)."

I propose that we move the entire tree that is using autoconf 2.5x to
autoconf 2.59 along with the corresponding one character update to
sourcebuild.texi file.

I could upload the regenerated files, if no-one objects.  I had been
running with AC 2.59 generated files in my local tree for a few weeks
now.

Kelley Cook