blas-f77 compatibility check

[John W. Eaton]

On  1-Apr-2008, Jaroslav Hajek wrote:

| there have been recently some issues concerning building Octave with
| BLAS libraries incompatible with the Fortran compiler used.
| The problem in question was triggered by a call to ZDOTC from
| qrupdate/zqrqhv.f. Currently, this is fixed by providing replacements
| for ZDOTU and ZDOTC in blas-xtra/xzdotc.f and blas-xtra/xzdotu.f, and
| changing the call in qrupdate/zqrhqhv.f to XZDOTC instead.
| 
| The attached changeset provides an alternative solution, that uses a
| new ACX_BLAS_WITH_F77_FUNC macro from Peter Simons'
| archive (see http://autoconf-archive.cryp.to/acx_blas_f77_func.html)
| instead of plain ACX_BLAS in configure.in, imposing the constraint
| that the BLAS library used for building Octave *must* be compatible
| with the Fortran 77 compiler, otherwise it is rejected.

I applied this changeset.

Thanks,

jwe