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CMake: Test Counting

Close #69 Unused Var: Warning

Fix #75 <complex> may define macro I

Fix #75 as described by undefining the macro `I` from `<complex>`
if defined (as in `glibc`).

This seems to be the only include of it.

Close #69
[This](http://stackoverflow.com/a/3418951)
stackoverflow post recommended
[that](http://herbsutter.com/2009/10/18/mailbag-shutting-up-compiler-warnings/)
Herb Sutter blog post with a general and portable solution and it
works great! :)

- automatically detect number of examples

Fix Compile Error: str Naming

This fixes a build error compiling with `nvcc/7.5` + `gcc/4.9.2`
causing a
```
./include/pybind11/pybind11.h(952): here

./include/pybind11/pytypes.h: In member function ‘pybind11::str pybind11::handle::str() const’:
./include/pybind11/pytypes.h:269:8: error: expected primary-expression before ‘class’
     return pybind11::str(str, false);
        ^
./include/pybind11/pytypes.h:269:8: error: expected ‘;’ before ‘class’
./include/pybind11/pytypes.h:269:8: error: expected primary-expression before ‘class’
```

- new pybind11::base<> attribute to indicate a subclass relationship
- unified infrastructure for parsing variadic arguments in class_ and cpp_function
- use 'handle' and 'object' more consistently everywhere