Fix type casted constants

This fixes a bug when using type casted constantes.

Consider the following swig file:
<pre>
%module Test
#define FOO 10000ULL
</pre>

Without the fix, the following is generated:
<pre>
  FOO = 10000ULL
</pre>
...which is invalid ruby code.

With the fix:
<pre>
  FOO = 10000
</pre>
FFI is responsible for casting the variable to the appropriate type when a function is called.