Rc2.1 , fixed c++bugs,fixed python wrapper bugs, and fixed clang++ compiler problems

- fixed some minor bugs in operator.hxx and accumulator.hxx:
  resize of functions with order==0 where wrong

- OpenGM compiles with clang++ for me on all targets i tested but one external target still fails:
    - Qpbo external still does not compile with clang
      Clang Error:
      /opengm/src/external/QPBO-v1.3.src-patched/instances.inc:30:28: error: 
      explicit specialization of   'get_type_information' after instantiation
      inline void QPBO<double>::get_type_information(char*& type_name, char*& type_format)


- Removed ALL warnings (default active)  with clang++ compiler and ninja build system on targets I tested (but not from external targets)
There are still some  **important** warnings in Maxflow external which  should be fixed.
An example is:

   opengm/src/external/MaxFlow-v3.02.src-patched/maxflow.cpp:367:16: 
   note: place parentheses around the   assignment to silence this warning
        if (i->parent = a0_min)

And some minor warnings in MRF lib:

src/external/MRF-v2.1.src-patched/GCoptimization.cpp:970:55: 
    note: place parentheses around the '&&' expression to silence this warning
    while (old_energy < 0 || old_energy > new_energy  && curr_cycle <= max_num_iterations)
make