maint: Refactor general/isXXX.m scripts to put input validation first. * general/isdir.m, general/isequal.m, general/isequalwithequalnans.m, general/isscalar.m, general/issquare.m, general/isvector.m: Refactor code to put input validation first. * general/iscolumn.m, general/isrow.m : Remove useless initialization of output variable. * general/isa.m: Add additional tests for various classes.

--- a/scripts/general/isequal.m
+++ b/scripts/general/isequal.m
@@ -24,12 +24,12 @@
 
 function retval = isequal (x1, varargin)
 
-  if (nargin > 1)
-    retval = __isequal__ (false, x1, varargin{:});
-  else
+  if (nargin < 2)
     print_usage ();
   endif
 
+  retval = __isequal__ (false, x1, varargin{:});
+
 endfunction
 
 ## test size and shape