Fix data dependence test on zero overlap functions

[Sebastian Pop]

Hi,

Here is the last fix for being able to pass bootstrap with
BOOT_CFLAGS="-g -O2 -fcheck-data-deps", i.e. comparing
the results of the existing data dependence analysis with the
results of the omega dependence solver.

This patch fixes a problem where the overlapping iterations are
set to zero, that means that:
- the data access functions are the same, and
- the evolution in the innermost loop is zero.
In that case the old data dep test answered correctly but incompletely
that there is a zero distance vector, and it missed the fact that there
is also a distance vector whose innermost component is set to 1.

The following example illustrates this problem:
  loop_1
    A[3] = ...
    ... = A[3]
  endloop_1
where we used to have a single distance vector: (0), and now we
also add the distance vector (1).

Bootntested on i686-linux with BOOT_CFLAGS="-O2 -fcheck-data-deps".
Committed to trunk.

Sebastian
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