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. * __dispatch__.cc, __dsearchn__.cc, __ichol__.cc, __lin_interpn__.cc, balance.cc, betainc.cc, bitfcns.cc, bsxfun.cc, cellfun.cc, colloc.cc, conv2.cc, daspk.cc, dasrt.cc, dassl.cc, data.cc, debug.cc, dirfns.cc, dlmread.cc, dot.cc, eig.cc, error.cc, fft.cc, fft2.cc, fftn.cc, file-io.cc, ov-type-conv.h: Use new C++ archetype in more files.

--- a/libinterp/corefcn/balance.cc	Wed Dec 16 17:09:44 2015 -0500
+++ b/libinterp/corefcn/balance.cc	Wed Dec 16 15:00:31 2015 -0800
@@ -91,13 +91,13 @@
 (SIAM Journal on Scientific and Statistical Computing, 1981).\n\
 @end deftypefn")
 {
-  octave_value_list retval;
-
   int nargin = args.length ();
 
   if (nargin < 1 || nargin > 3 || nargout < 0)
     print_usage ();
 
+  octave_value_list retval;
+
   // determine if it's AEP or GEP
   bool AEPcase = nargin == 1 || args(1).is_string ();