build break on compute-dialog.c with VPATH build

[Ben Pfaff]

When I do
     mkdir _build
     cd _build
     ../configure
     make
the build breaks on compute-dialog.c here:
     #include <language/expressions/parse.inc>
because $(top_builddir)/src is not in the include path.

One solution would be to change this line to:
     #include <../../language/expressions/parse.inc>
but frankly I don't like the idea of including this file here at
all.  It puts a second copy of the functions array into the
binary, for one thing, and it breaks encapsulation, for another?

Why not just export a few accessor functions from the expressions
code?  I thought we talked about that approach before, and I
don't remember anyone pointing out why it wouldn't work.

-- 
"J'avais trouv'e ma religion :
 rien ne me parut plus important qu'un livre.
 La biblioth`eque, j'y voyais un temple."
--Jean-Paul Sartre