ISIS >=1.6.1-5 does not provide the finite function any more

   finite(x)
should actually be replaced by
   not(isinf(x) or isnan(x))
and not as stated in the commit message below:

commit 79e98314fa2c9f363b795a5781f12ac707aa083a
Author: John C. Houck <houck@space.mit.edu>
Date:   Thu Jul 15 08:39:26 2010 -0400

    remove various obsolete functions

       * these are provided by slang:
          any, cumsum, hypot, max, min, shift, sum

       * these are available under a different name:
          iback_fun    (now back_fun)
          _define_bgd  (now _define_back)
          define_bgd   (now define_back)
         The obsoleted names have printed a warning message for
         years.  As of now, the obsoleted names have been removed

       * The 'finite' function has been removed.  It was probably
         not used much, and is easily replaced:
            finite(x) -> wherenot (isinf(x) or isnan(x))