Improvements needed for sage:

- the architecture-independent files that are built (such as example outputs
  and html documentation, should be put into ./BUILD/share, and should not be
  rebuilt if architecture-dependent files are updated.  However, after an error
  in building the architecture-dependent files, it should not try to build the
  architecture-independent files, even if make -k was typed.  This will allow
  our source code optionally to be shipped with the architecture-dependent
  files, which should speed upbuilding.  We could even include that on the web
  site.

- back up to autoconf 2.59, instead of 2.61

