#93 SLAB not using absolute values

[seismick]

This process does not do what is claims to do.
The help for SLAB says:
! Allowed = MED (Median of sample absolute values.)
! Allowed = AVE (Average, or arithmetic mean, of sample absolute values.)
! Allowed = LAV (Largest sample absolute value.)
! Allowed = RMS (Square root of mean square of sample absolute values.)

However, the absolute value is not used, except for LAV. RMS will not be
affected, but the AVE and MED will tend to zero, for long windows anyway.
That may be useful to some people, but I think for most users, the
usual attributes would be average absolute and median absolute.
So the best solution is keep the existing attributes and also to offer
2 more options: median of absolute values and mean of absolute values
(aka L1 norm). I have modified the subroutine slab_solve to compute
these attributes. The array obj%opt_stat is also augmented for the
extra options in slab_struct and the slab_update subroutine.

The attached file slab.f90 will offer the corrected attributes, and
also edited documentation. So EZGUI should be run to update the xml
file to include the modified help.

[Bill Menger]

changed and tested in a few modes.