Dear all,

the attached patch implements vector sections in DATA statements.

The implementation is simpler than the size of the patch suggests,
as part of changes try to clean up the existing code to make it
easier to understand, as ordinary sections (start:end:stride)
and vector sections may actually share some common code.

The basisc idea of the implementation is that one needs a
temporary vector that keeps track of the offsets into the
array constructors for the indices in the array reference
that are vectors.

Regtested on x86_64-pc-linux-gnu.  OK for mainline?

Thanks,
Harald