Octave: add support for version 4.2

- .travis.yml:
  - ppa:kwwette/octaves has Octave version 4.2, also run C++11 tests
- configure.ac:
  - prefer Octave program "octave-cli" to "octave"
  - extract any -std=* flags from CXX, add to OCTAVE_CXXFLAGS
- Lib/typemaps/fragments.swg:
  - SWIG_isfinite_func(): extern "C++" is required as this fragment can
    end up inside an extern "C" { } block
- Lib/octave:
  - add std_wstring.i (copied from std_string.i) for C++11 tests
- Lib/octave/octrun.swg:
  - move Octave version-checking macros to octruntime.swg
  - Octave single()/double() functions now call .as_single()/.as_double()
    methods; redirect calls to __float__() method as per .scalar_value()
  - << and >> operators are no longer supported by Octave
- Lib/octave/octruntime.swg:
  - move Octave version-checking macros here for conditional #includes
  - #include interpreter.h instead of #toplev.h
  - #include call-stack.h (now needed for octave_call_stack)
  - unwind_protect is now in octave:: namespace
  - error_state and warning_state are deprecated; use try/catch to catch
    errors in feval() instead
  - always set octave_exit = ::_Exit, to try to prevent segfault on exit
- Lib/octave/octopers.swg:
  - << and >> operators are no longer supported by Octave
- Lib/octave/exception.i:
  - Add macro SWIG_RETHROW_OCTAVE_EXCEPTIONS which rethrows any
    exceptions raised by Octave >= 4.2
- Examples/test-suite/exception_order.i:
  - Use macro SWIG_RETHROW_OCTAVE_EXCEPTIONS to rethrow exceptions
    raised by error() function in Octave >= 4.2
- Update Doc/Manual/Octave.html and CHANGES.current

CHANGES.current

@@ -7,6 +7,30 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 3.0.12 (in progress)
 ============================
 
+2017-01-22: kwwette
+            [Octave] add support for version 4.2
+            - The Octave API now uses some C++11 features. It is recommended to use
+              the mkoctfile program supplied by Octave to compile the SWIG-generated
+              wrapper code, as mkoctfile will ensure the correct C++ compiler/options
+              are used. Otherwise, the value of `mkoctfile -p CXX` should be parsed
+              for any -std=* flags which might be present.
+            - Octave has dropped support for << and >> operators, so SWIG now
+              ignores them.
+            - The Octave error() function now raises C++ exceptions to propagate
+              Octave errors, so %exception directives may need to be modified.
+              For convenience the SWIG_RETHROW_OCTAVE_EXCEPTIONS macro can be used
+              to rethrow any Octave exceptions for Octave itself to handle, e.g.:
+
+                try {
+                  $action                        // may call error()
+                }
+                SWIG_RETHROW_OCTAVE_EXCEPTIONS   // error() exceptions are rethrown
+                catch(...) {
+                  ...                            // all other exceptions
+                }
+
+            *** POTENTIAL INCOMPATIBILITY ***
+
 2017-01-16: wkalinin
             [C#] Fix #733 regression introduced in swig-3.0.9.
             Missing virtual function override in C# layer when using %import.