Matching corresponding types between host and device

All over the documentation and in the tests we use fundamental C++ types like `int`, `short`, `long`. That may cause problems when their sizes do not match sizes of OpenCL types with the same names.

In particular, I'm talking about `long`. It's common that on 32-bit OSs `sizeof(long) == 4` but for OpenCL `long` type `sizeof(long) == 8'. Example of code that will fail on 32-bit systems:

``` cpp
boost::compute::vector vec(...);
boost::compute::transform(
vec.begin(), vec.end(), vec.begin(), boost::compute::identity()
);
```

Error that we would probably get:

``` bash
/Users/travis/build/haahh/compute/include/boost/compute/detail/meta_kernel.hpp:451:19: error: no matching function for call to 'type_name'
stream << type_name();
^~~~~~~~~~~~~~~
/Users/travis/build/haahh/compute/include/boost/compute/detail/meta_kernel.hpp:375:19: note: in instantiation of function template specialization 'boost::compute::detail::meta_kernel::type' requested here
stream << type() << " " << name;
(...)
```

This is because we do not define `type_name()` but probably `type_name()` as in this case C++ `long long` is OpenCL `long`

I think we have to ways to fix that (if you think that needs to be somehow fixed):
- We can put a note/warning about this problem with types in documentation instructing users to use `boost::compute::_` types (or just to have that issue in mind) and change all types in test to `boost::compute::_` that have correct size (`long` --> 'boost::compute::long_` ).
- We can define correct `type_name()` for every fundamental C++ based on their real size, so if `sizeof(long) == 4` then `type_name()` returns `"int"` string.
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