compatibility patch of isfield

[Andy Adler]

In Matlab, isfield gives output 0 for all
unreasonable inputs, rather than showing an error.

Examples:
    >> a.b=1;
    >> x=0;
    >> isfield(x,0)
    ans =
         0
    >> isfield(a,0)
    ans =
         0
    >> isfield(a,'b')
    ans =
         1
    >> isfield(a)
    ??? Input argument 'f' is undefined.

    Error in ==> C:\Program Files\MATLAB6p5\toolbox\matlab\datatypes\isfield.m
    On line 12  ==>   tf = any(strcmp(fieldnames(s),f));

--
Andy Adler

Here is a patch:

$ cvs diff -u src/ov-struct.cc
RCS file: /cvs/octave/src/ov-struct.cc,v
retrieving revision 1.48
diff -u -r1.48 ov-struct.cc
--- a/src/ov-struct.cc  12 Mar 2004 19:13:02 -0000      1.48
+++ b/src/ov-struct.cc  25 Jul 2004 14:02:14 -0000
@@ -679,7 +679,7 @@
          retval = m.contains (key) != 0;
        }
       else
-       print_usage ("isfield");
+       retval= 0;
     }
   else
     print_usage ("isfield");