maint: Use new C++ archetype in more files. Place input validation first in files. Move declaration of retval down in function to be closer to point of usage. Eliminate else clause after if () error. Use "return ovl()" where it makes sense. * find.cc, gammainc.cc, gcd.cc, getgrent.cc, getpwent.cc, givens.cc, graphics.cc, help.cc, hess.cc, hex2num.cc, input.cc, kron.cc, load-path.cc, load-save.cc, lookup.cc, mappers.cc, matrix_type.cc, mgorth.cc, nproc.cc, ordschur.cc, pager.cc, pinv.cc, pr-output.cc, profiler.cc, psi.cc, quad.cc, rcond.cc, regexp.cc, schur.cc, sighandlers.cc, sparse.cc, str2double.cc, strfind.cc, strfns.cc, sub2ind.cc, svd.cc, sylvester.cc, symtab.cc, syscalls.cc, sysdep.cc, time.cc, toplev.cc, tril.cc, tsearch.cc, typecast.cc, urlwrite.cc, utils.cc, variables.cc, __delaunayn__.cc, __eigs__.cc, __glpk__.cc, __magick_read__.cc, __osmesa_print__.cc, __voronoi__.cc, amd.cc, audiodevinfo.cc, audioread.cc, chol.cc, colamd.cc, dmperm.cc, fftw.cc, qr.cc, symbfact.cc, symrcm.cc, ov-bool-mat.cc, ov-cell.cc, ov-class.cc, ov-classdef.cc, ov-fcn-handle.cc, ov-fcn-inline.cc, ov-flt-re-mat.cc, ov-java.cc, ov-null-mat.cc, ov-oncleanup.cc, ov-re-mat.cc, ov-struct.cc, ov-typeinfo.cc, ov-usr-fcn.cc, ov.cc, octave.cc: Use new C++ archetype in more files.

--- a/libinterp/corefcn/mgorth.cc	Fri Dec 18 16:22:53 2015 -0500
+++ b/libinterp/corefcn/mgorth.cc	Fri Dec 18 15:37:22 2015 -0800
@@ -67,8 +67,6 @@
 \n\
 @end deftypefn")
 {
-  octave_value_list retval;
-
   if (args.length () != 2)
     print_usage ();
 
@@ -77,16 +75,13 @@
 
   if (arg_v.ndims () != 2 || arg_x.ndims () != 2 || arg_x.columns () != 1
       || arg_v.rows () != arg_x.rows ())
-    {
-      error ("mgorth: V should be a matrix, and X a column vector with"
-             " the same number of rows as V.");
-      return retval;
-    }
+    error ("mgorth: V should be a matrix, and X a column vector with"
+           " the same number of rows as V.");
 
   if (! arg_x.is_numeric_type () && ! arg_v.is_numeric_type ())
-    {
-      error ("mgorth: X and V must be numeric");
-    }
+    error ("mgorth: X and V must be numeric");
+
+  octave_value_list retval;
 
   bool iscomplex = (arg_x.is_complex_type () || arg_v.is_complex_type ());
   if (arg_x.is_single_type () || arg_v.is_single_type ())