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/sylvester.cc	Fri Dec 18 16:22:53 2015 -0500
+++ b/libinterp/corefcn/sylvester.cc	Fri Dec 18 15:37:22 2015 -0800
@@ -60,11 +60,11 @@
 @end example\n\
 @end deftypefn")
 {
-  octave_value retval;
-
   if (args.length () != 3)
     print_usage ();
 
+  octave_value retval;
+
   octave_value arg_a = args(0);
   octave_value arg_b = args(1);
   octave_value arg_c = args(2);
@@ -88,9 +88,9 @@
 
   if (arg_a_is_empty > 0 && arg_b_is_empty > 0 && arg_c_is_empty > 0)
     if (isfloat)
-      return octave_value (FloatMatrix ());
+      return ovl (FloatMatrix ());
     else
-      return octave_value (Matrix ());
+      return ovl (Matrix ());
   else if (arg_a_is_empty || arg_b_is_empty || arg_c_is_empty)
     return retval;