Don't save "warning: " prefix in lastwarn() message. * error.cc (vwarning): Save base_msg (without "warning: ") to Vlast_warning_message. * error.cc (error_1): Use std::string operators rather than strsave to strip "\n" from fmt string. Simpler syntax avoids having to delete [] memory created with new. * error.cc (warning_1): Strip trailing newline from fmt string as error_1 does. * fail.m: Fix input validation which allowed nonsensical second input with 3 args. Don't post-process warning or error messages from lastwarn or lasterr. Add BIST test for input validation.

%!function r = f1 ()
%!  ls = svd (1);
%!  r = eval ("ls -1;");
%!endfunction
%!function r = f2 ()
%!  [u,ls,v] = svd (1);
%!  r = eval ("ls -1;");
%!endfunction
%!function r = f3 (ls)
%!  r = eval ("ls -1;");
%!endfunction

%!test
%! ## Windows systems can't run "ls -1"
%! if (! ispc ())
%!   assert (f1 (), 0);
%!   assert (f2 (), 0);
%!   assert (ischar (f3 ()), true);
%!   assert (f3 (1), 0);
%! endif