[Changeset] Add the rcond function

On 14-May-2008, David Bateman wrote:

| Although this changeset is large, most of its just replacing "rcond"
| with "rcon" to avoid shadow warnings for the rcond methods that the
| changeset introduces in Matrix and ComplexMatrix classes. The oct-file
| itself is then trivial.

I applied this changeset.

| Note that although I started doing the same methods for sparse matrices,
| matlab doesn't support this and so I didn't do it in the end. Use
| condest(a) if the matrix "a" is sparse.. Also it appears that matlab
| only uses the LU factorization for their rcond function and not the
| hermitian or triangular matrix versions of the LAPACK factorizations.
| Therefore the Octave code will be faster for these cases, but won't
| necessarily return the same result as matlab. This is a 1-norm estimate
| of the reciprocal condition number in any case and so I believe the
| difference can be ignore as its not the exact value we are interested by
| rather its magnitude.

OK.

Thanks,

jwe